Unlike Marvel vs. Capcom 2 which had stage-specific themes, Marvel vs. Capcom 3 returns to the character-based themes from Marvel vs. Capcom 1.
All of these themes are incredibly awesome and techno-based, so give them all a listen!
http://www.eventhubs.com/news/2010/oct/22/character-themes-marvel-vs-capcom-3/ This is obviously not a complete soundtrack: the entire roster is still about half-full right now.