Here are last weeks top ten Arcade Titles played over Xbox live -

1 Portal: Still Alive
2 Penny Arcade Episode Two
3 Castle Crashers
4 Are You Smarter Than a 5th Grader
5 Fable II Pub Games
6 Duke Nukem 3D
7 Age of Booty
8 UNO
9 MEGA MAN 9
10 Braid

These are based on games purchased rather than demo versions.

Source