Straight from Major Nelson's blog....

Xbox 360 Top Games
1 Saints Row
2 Call of Duty 2
3 Madden NFL 07
4 Test Drive Unlimited
5 Ghost Recon 3
6 DEAD RISING
7 Oblivion
8 BFMC
9 Texas Hold 'em
10 final fantasy XI

Top Arcade Titles (Full Versions)*
1 Texas Hold 'em
2 Street Fighter II' Hyper Fighting
3 Hexic HD
4 Geometry Wars Evolved
5 UNO
6 Scramble
7 PAC-MAN
8 Marble Blast Ultra
9 Bankshot Billiards 2
10 Zuma

*This only counts games that are purchased, not demos

Original Xbox Top Games
1 Halo 2
2 Madden NFL 07
3 Battlefield 2: MC
4 Pro Evolution Soccer 5
5 Counter-Strike
6 Splinter Cell Chaos
7 Star Wars: Battlfrnt 2
8 Rainbow Six 3 BA
9 Forza Motorsport
10 Ghost Recon 2: SS