Depends on what I'm feeling. Alien used to be the perfect therapy for the angry teenage me, while Terria favorites "Nobody's Here" and "Stagnant" were my big "I'm sad" songs.

Nowadays, I use Devin to remind me of the insanely happy moments in life. "Kingdom", "Numbered!", "Awake!!", and "Hypergeek" work well. When I'm feeling a little down, "Bastard" helps.

I generally just listen to the Terria album, as it seems to work best; that and The Hummer.
That said, if I were to pick a varied playlist, I'd go with:

Earth Day
Suicide
Deep Peace
Nobody's Here
Bastard
The Death of Music
Planet Rain
Heaven Send
Supercrush!
Pixillate
Unity
The Abacus

Devin's music definitely helps me in certain situations, though instead of certain songs its certain albums that help or enhance different things (disclaimer: these are my opinions of the albums).

City: Works well for purging anxiety
Biomech: Great for when you're feeling really down, also good for driving during the night
Alien: As cheesy as it sounds, great for when you don't even feel human (sort of out of your mind mentally (without drug use))
Terria: A great uplift for one's day in my opinion
The Hummer: Personally helps me drift off to sleep or study to
Accelerated Evolution: Makes driving on a sunny day seem pretty calming

I have most of the other albums but they don't work in a specific way for me