Straight from Major Nelson's blog, here are the top Xbox Live games for the week of 6/12/2006:
Xbox 360 Top Live Games
1 Call of Duty 2
2 Ghost Recon 3
3 Oblivion
4 BFMC
5 Final Fantasy XI
6 EA SPORTSâ„¢ Fight Night Round 3
7 Perfect Dark Zero
8 PGR3
9 dead or alive 4
10 Hitman: Blood Money
Original Xbox Top Live Games
1 Halo 2
2 Battlefield 2: MC
3 Counter-Strike
4 Splinter Cell Chaos
5 Rainbow Six 3 BA
6 Star Wars: Battlfrnt 2
7 Pro Evolution Soccer 5
8 Madden NFL 2006
9 Forza Motorsport
10 Ghost Recon 2: SS
The Major also points out that if you were to combine the two lists into one, that Halo 2 would be the most played Xbox Live game (surprise) followed by all of the 360 games.