The entire soundtrack, for reference:

http://dbsoundworks.bandcamp.com/album/super-meat-boy-soundtrack

I've been listening to it a lot lately as I've been doing quite a bit of painting, and I'm continually reminded of how damn good it is. I know Betus Blues got a lot of love, but I tend to lean toward Hot Damned as being the most mind blowing track. Those runs are just insane. In terms of pure, gamey soundtracks, I hold this compilation of tracks in as high of regard as Nintendo's early work. The remixes, the chip tunes, the medley that plays during the credits... it's all so spot on for a game like Super Meat Boy. And almost a year after I finished the game, I'm still listening to it and picturing the levels... I can't quit you, Meat Boy.

Power of the Meat is fantastic

I really like the style of SMB's OST, and I prefer Dr. Fetus' Castle the best, it remind me of some classic NES game musics.

4-bit Meat Boy Theme

So DIRTY!

I literally can't not smile if McLarty Party People is playing and I'm not actually playing the game. Though usually I'd probably still argue for Betus Blues.

Also, while kind of different from the rest, Can O' Salt is excellent.

C.H.A.D's Broken Wind. One of the Dark World bits of music, 2 I think. It was playing on a level and I was taking a break with Meat Boy sitting at the start of a level. I had one of those "Man, I LOVE this game!" moments I guess that's why that particular piece has stuck with me.