Please note that the dates are subject to change, so without further ado, here is the list:

1 Dec 2009:

Rogue Warrior
Avatar
MX Vs ATV: Reflex

8 Dec 2009:

The Saboteur

17 Dec 2009:

Blue Toad Murder Files (PSN)

22 Dec 2009:

Guitar Hero Van Halen

Expected in December:

PixelJunk Shooter
Scene It? Bright Lights! Big Screen!
Buzz! Quiz World (PS3 & PSP)

A slightly dry month for gaming, but there are a couple of games that stand out e.g. PixelJunk Shooter and The Saboteur. Makes you wonder why everyone delayed all their games into 2010, when there are very few big releases in December.