bear in mind for tightness, latency always rears it's ugly head, so be careful, might be worth recording the unaffected guitar first and putting the plugin on afterwards

although u could always download some aiso drivers to make it a bit better but still not perfick.

Paul
http://www.myspace.com/stinkweedband

I like Bombfactory's Sansamp plugin and Amp Farm.

Massey's THC protools plugin is pretty interesting as well.

I'm not a big fan of distortion pedals. Just give me the good old gain-channel of a (good!) amp.
On the other hand, an Ibanez TubeScreamer (or Maxon, much cheaper, same quality) will give you a lot of extra punch. Very useful to create the high attack sound, like Fear Factory or Meshuggah.

If you MUST use a distortion pedal, I'd go for a Pro Co Rat, or even the Pro Co Solo. Check 'em out, very nice stuff. Not too expensive.

http://www.procosound.com