Guitars:
2. Herman Li (DragonForce) technically almost over the top

Have you ever seen them play live? Hit and miss yo!

Yeah I saw them live twice. Of course it's nowhere near the sound they generate in the studio, yet it was good.
At least for me it was satisfying.

That's most cliched kind of thread evar

but well, let's whore up my post count.

Gitters:

Mikael Akerfeldt of Opeth - I like how he puts together all that unusual harmonies and admits that he don't know chord names and stuff. Also, pretty flawless live.
Bulb of Periphery - for being well, Bulb.
Fredrik Thordendal (Marten too, heard he wrote lots of their stuff) of youknowwhat - for setting off whole djent movement and all that groovey things
Santiago Dobles of Aghora - smooth riffage and shred without being wanky, just listen to last Aghora record, it's fantastic
Drop of Sybreed - dunno if top guitarist, top songwriter for sure, and with pretty strong fingers I guess (17-68 strings @ drop Bb)

Basses:

Sean Malone (Aghora, Gordian Knot, Cynic etc) - that's a guy with a recognizable style, can be technical and groovy at the same time
Geddy Lee - awesomely technical basslines neatly composed into catchy songs, that's quite a thing. Dude with such skillz being a frontman and not shoving his bass-penis (well, no solos) into the audience's faces is also quite rare I think.
Les Claypool of Primus - turned the music inside out then laughed in everyones face, pretty mandatory choice.

I can't think about more bassists to be honest, can't differ them that much (should've listen more funk I guess). Every that fits in the band and doesn't do solos is good in my book.

Drums:

Morgan Agren from Mats/Morgan, Kaipa and others - because, whoah
Jojo Mayer of Nerve - because, WHOAH. That's more impressive that any ultrafast metal performance I've seen.
Stef Broks of Textures - drums = foundament of good djent, and he delivers. Also, makes impression he doesn't break a sweat when playing, just like
Gene Hoglan - self explanatory
Mario Duplantier - because he does MASSIVE THINGS

There's more, drummers are probably my favourite kind of musicians, shame about the 5 limit

Vocals:

The Dev - who else, best dynamics in voice evar
Erik Kalsbeek of Textures - excellent clean vocals
Mikael Akerfeldt - great growls and cleans, basically perfect all round vocalist.
That Linkin-Park dude on drugs from Scarve - because he's crazy.
Randy Blythe for Lamb of God - most convincing Menacing Screamy Bloke I've ever heard.

Since the forums were down yesterday I'll do this today:

Vocals:
Dev - I guess it's obligatory right? But then again I'm sure we all adore his vocals
Mikael Akerfeldt - He just has the best death growl ever and the softest singing voice, amazing.
Steven Wilson - His vocals fit so well over everything he's done musically. He did so good on Bleak.
The dude from Between the Buried and Me(forgot his name) - his style is so good. He belts those growls/screams out so well live, so much passion in his deliverance of both kinds of vocals.
Karl Schubach (Misery Signals) - He just has such a brutal voice, especially on Controller, and a pretty good singing voice. Love his lyrics and style.

Guitars: (this list could go on and on but i'll limit myself)
Mikael Akerfeldt - His writing is just unparalleled, his solos fit everything he writes almost too well, and the fact he can play and sing their stuff at the same time gives him major points.
Bob Zabek - Simply amazing, in my opinion possibly one of the best guitarists to ever live.
Marc Okubo (Veil of Maya) - The dude may be one of the most original metal guitarists in years. The stuff he writes is just crazy.
Bill and Brent (Mastodon) - These guys have been a constant inspiration to me ever since I first heard "March of the Fire Ants" so many years ago.
Wes Borland - Needless to say, this guy is definitely one of my favorites, if it werent for him I probably wouldnt be into 2 handed tapping stuff like I am today. Plus I dig his vocals in Black Light Burns

Bass:
Arif (dont know his last name, from Protest the Hero) - This guy fucking rips. He knows when to play a little extra on the bass and he knows when to hold down the rhythm nicely. He is astounding, especially live.
Martin Mendez(Opeth duh) - His bass lines accompany their music so well its disturbing.
Geddy Lee - I grew up listening to Rush, the guy is still amazing today(maybe not on the vocals as much...lol)
Timmy C (Rage Against the Machine/Audioslave) - He knows how to fucking play bass, really well! haha
The last is a toss up between the dude from Between the Buried and Me and Les Claypool, both amazing, Claypool obviously wins in the "originality" catagory.

Drums:
Morgan Agren - Anyone who has listened to "Sol Niger Within" will know why.
Tomas Haake - The man is a machine. He is utterly perfect live and his drumming is just too good.
Gene Hoglan - We all know why, all of his stuff is incredible!
Neil Peart - Again, I grew up with Rush and he is still one of the best drummers out there.
Gavin Harrison - He can do it all. The guy is probably the most well versed drummer out there, and he plays 2 handed tap guitar! Big plus in my book!

Honorable mentions for guitar: Mattias Eklundh, Guthrie Govan, Tosin Abasi, Joe Satriani, Alex Lifeson, Christofer Malmstrom/Klas Isberg(Darkane), The Dev Man(of course, he was next in line for the list), Josh Homme (Queens of the Stone Age, Eagles of Death Metal, also in the running for vocals), The dude from Fall of Troy, Tim Millar from Protest the Hero, Paul/Dusty from Between the Buried and Me.

Ok I'll stop now...

Here we go.... thought I'd join in on the fun...

Vocals:

1. Dev - Hands down my favorite, not cuz I play with him either. The guy has the most brilliant melodies and great lyrics.
2. Mike Patton (FNM, Mr. Bungle) - A very, very, very close second if not tied with Dev for the same reasons.
3. Phil Anselmo (Pantera Era) - If it wasn't for him, a lot of Metal singers today would sound like pussies! Powerful and real, no bullshit vocalist.
4. Chris Cornell (Soundgarden Era) - I'm talking about the "Badmotorfinger" days. This guy was unbelievable and I loved everything he did with Soundgarden.
5. Mikael Akerfeldt (Opeth) - Best "Demonic Growl" in Metal and an awesome clean voice.

Guitar:

1. Dimebag Darrell (Pantera) - By far... my favorite of all time. You could tell Dimebag's playing in a second, he had his own style going on that was unforgettable.
2. Eddie Van Halen (Van Halen) - Again, got his own style and he influenced so many guitarist's in rock/metal today.
3. Dev - Hands down the best guitar player I've ever had the pleasure of playing with on any album I've been part of and he's right up there with my top two.
4. Fredrik Thordendal (Meshuggah) - This guy's a freak! Insane rhythm playing and just as crazy leads, not to mention an awesome songwriter.
5. Mark Morton (Lamb of God) - this guy is by far my new favorite modern guitar player. His solo's on "Wrath" and rhythm playing are sick.

Bass:

1. Les Claypool (Primus) - Need I explain..... the guy's insane.
2. Trevor Dunn (Mr. Bungle, Fantomas) - So creative, killer tome and very versatile.
3. Geddy Lee (Rush) - So influential to so many Bass Players and just great ideas.
4. Michael Manring - This guy is a freak!!! Such a crazy Bass Player.
5. John Myung (Dream Theater) - It blows my mind that he duplicates what the guitar does in those songs. Amazing player and fun to watch his fingers go!

Drums:

1. Gavin Harrison (Porcupine Tree) - Hands down my biggest influence right now and probably the smoothest, most versatile and talented drummer out there.
2. Neil Peart (Rush) - He was my biggest influence growing up, hands down.
3. Vinnie Paul (Pantera)- The reason I have a heavy groove and started double bass drumming is because of this guy. The king of groove in Metal Drumming period!
4. Tomas Haake (Meshuggah) - Come on.... this guy on a bad night destroys most drummers in the world. His beats and fills are SICK!
5. Tim Alexander (Primus) - This guy is the reason I play as many cymbals as I do and the reason for the whacked out cymbal influenced beats I play in many different projects. HUGE influence!
6. I could list another 5 drummers easily.... of course.... but these top 5 never leave my mind, they all have influenced me big time and there really is no order in which I list these guys over one another. Had to be said.....

Good stuff dude! We see eye to eye on a lot of levels! haha

2. Trevor Dunn (Mr. Bungle, Fantomas) - So creative, killer tome and very versatile.

definitely. he just missed out on my list. i saw him play with the melvins and we was amazing. he fit right in with buzz and dale

Vocalists:
Devin Townsend
Jeff Buckley
Mike Patton
Tim Bowness (No-man)
Janis Joplin

Drummers:
Vinnie Colaiuta (Too much too count, played with Frank Zappa, Jeff Beck, Sting and mooore)
Gavin Harrison (Porcupine Tree)
Yoshida Tatsuya (Ruins, Koenjihyakkei)
There is not much drummers that could compete with those so that's the reason I'm out of names:))

Bassists:
Trevor Dunn(more for his ideas:D) (Secret Chiefs 3, Electric Masada)
Mark Sandman (Morphine)
Roger Waters (more as a singer-songwriter:D) (Pink Floyd of course)
Colin Edwin (Porcupine Tree)
Geddy Lee. Yes Geddy Lee:) ( Rush)

Guitarists:
Frank Zappa (but more as a composer)
Omar A. Rodriguez-Lopez (The Mars Volta)
Adrien Belew (King Crimson)
John McLaughlin (goddamn, he's a genius)
Neil Young

Guitarists:
Michael Amott (Carcass, Arch Enemy, Spiritual Beggars) My personal biggest influence. Very versatile player and writer, and one of the few modern metal guitarists who realise it's usually more appropriate to play slower leads rather than shredding your fingers off.
James Hetfield (Metallica) Countless memorable riffs and leads, and still going strong after 25 years.
Miika Tenkula (Sentenced) Great composer, really knows how to take simple things and make them work together seamlessly to make good songs. R.I.P.
Slash (GNR, Velvet Revolver) The one and only true rock and roll guitar hero.
David Gilmour (Pink Floyd) So soulful, unbeatable at what he does.

Vocalists:
Mike Patton (Faith No More, etc...) Unbeliavably versatile.
Devin Can convey anything from fragile moments to pure rage, and does it so awesomely.
Dio Legend.
Mikael Stanne (Dark Tranquillity) Definitely one of the best modern metal singers, nails both the growls and clean parts.
Ville Laihiala (Sentenced) Great tone to his voice, and can communicate a nice range of emotions with a convincing delivery.

Bassists:
Cliff Burton (Metallica) His approach to the bass was completely new at the time.
Sean Malone (Cynic, etc.)
Billy Gould (Faith No More, etc)
Flea (RHCP)
Geddy Lee (Rush)

Drummers:
Gene Hoglan (SYL, etc.) The heaviest drumming ever.
Dave Lombardo (Slayer, etc.) In addition to being one of them who created metal drumming, he's great at all kinds of stuff.
Peter Wildoer (Darkane, etc.) Great solid versatile drummer.
Ken Owen (Carcass) Brought some fresh stuff into extreme metal drumming and has influenced countless other drummers.
Daniel Erlandsson (Arch Enemy, etc.), Adrian Erlandsson (At the Gates, etc.) These brothers both simply fucking rule. Creative and heavy.

Bonus: Top 1 Keyboardists
Kevin Moore (Dream Theater, Chroma Key, OSI) The best keyboardist Dream Theater ever had; I've always had this feeling he was the one who kept the band from going too far into instrumental wankery, since that's what they started doing after he left.

Vocalists:
Ville Laihiala (Sentenced) Great tone to his voice, and can communicate a nice range of emotions with a convincing delivery.

And Poisonblack!

Vocalists:
Tim Bowness (No-man)

good to see this guy on someone else's list. Definitely underrated.