It looks as if the recent Mythic Map Pack launch is still helping Halo 3 hold steady in that #1 spot. From Major Nelson’s blog-

Xbox 360 Top Live Titles (based on UU’s)

1    Halo 3
2    Call of Duty: WaW
3    Call of Duty 4
4    Gears of War 2
5    GTA IV
6    UFC 2009 Undisputed Demo
7    FIFA 09
8    Left 4 Dead
9    Fallout 3
10    Fable II

Top Arcade Titles (Full Versions purchased)

1    Brain Challenge
2    Castle Crashers
3    Star Trek: D•A•C
4    Hasbro Family Game Night **
5    Peggle
6    Worms
7    Space Invaders Extreme
8    UNO
9    Teenage Mutant Ninja Turtles 1989 Classic Arcade
10   ARKANOID Live!

The above arcade list is based on full versions purchased.
**Combined sales of all Hasbro Family Game Night titles