The multiplayer on Marble Blast never gets old, for me. I liked the single player on it, too.
I still play ranked matches on Street Fighter II, and if you like it, there's always a match available. I play MK3 less, but still give it a go once in a while.
Geometry Wars is always there taunting me with those last couple Achievements, and it's one of those classic games I'll always come back to for one more crack at a personal high score.