Tekken Tag's soundtrack is amazing. This game mixed up "partying" with skill-intensive movement based gameplay like no other. And it was also my first PS2 game so my jaw dropped. The hype was 11 out of 10. One of my favorite tracks is school theme:

The soundtracks' one "flaw" was that they were too groovy, so not as wide an emotional range as many other fighting games. But it isn't really a flaw considering it's a celebration kind of game. The music is just perfect for the game's movement system. Every moment felt like you were dancing.

My favorite Street Fighter soundtrack gotta be Cammy's theme:

I was never big into Street Fighter, but this track's opening gets me somewhat emotional every time for some reason. It's so good.

Classic MK music oozed atmosphere and sinister energy. Loved it. One of the most memorable ones for me is The Bridge:

Street Fighter II is the background music of my childhood — so much, in fact, that I typically take its greatness for granted. But when you line up the individual tracks like this...it's overwhelming. One of the best video game soundtracks, no question.

The one I remember the most (International Karate+/Amiga/'88):

SSB hands down (opening to Brawl in particular)

But that is kind of cheating since along with original tunes SSB has access to basically the entire nintendo music catalogue and in Ultimates case also music from other non nintendo franchises

Capcom vs. SNK 2 had a great soundtrack. Here are a couple of my favorites.

Fight Your Way (Nairobi)

Fight With The Wind (Kinderdijk)

This Is True Love Makin' (London)