From Major Nelson's Blog…
Xbox 360 Top Live Games
1 Call of Duty 2
2 DEAD RISING
3 Ghost Recon 3
4 Chromehounds
5 Oblivion
6 NCAA 07
7 BFMC
8 Final Fantasy XI
9 Dead Rising Demo
10 Lord of the Rings: BFME2
Original Xbox Top Live Games
1 Halo 2
2 Battlefield 2: MC
3 Splinter Cell Chaos
4 Counter-Strike
5 Pro Evolution Soccer 5
6 Rainbow Six 3 BA
7 Madden NFL 2006
8 Star Wars: Battlfrnt 2
9 Forza Motorsport
10 Rainbow Six 3
As always, if you were to combine the lists, Halo 2 would be number one with all of the Xbox360 games right behind it.