I have a 360 but I love to play older fighters like MVC2, SF, R.Schools, Bloody Roar, and Power Stone.
What do you mean by buy from XBL? Do you mean downloadable XBLA stuff? If so it’s just Fatal Fury Special, Hyper Fighting and Ultimate Mortal Kombat 3 until Super Turbo HD and Samurai Shodown 2 come out.
If you’re talking about retail games that work on Xbox 360 too, just look at my old and dead XBL Matchmaking Thread for a list of XBL compatible fighters.
Soul Calibur 1 is also on the way.
And there’s also that Yie Fu (name?) if you count that as a fighting game.
#Reload on the way as well