I adore using XBLA. I have like 40 games in total for it. It's great because I can be playing a game like Fallout 3 for a substantial amount of time, and when I want to play something different for a while, I just play an Arcade game. It means I can have a single disc in my 360 for weeks at a time.

I'm also a big fan of Steam, and one of the principle reasons for me wanting to get a PS3 at some point is for downloadable games like WipeOut HD, Warhawk, Shatter, Trine and the PixelJunk games.