I got a 120hz monitor the other day. I haven't had problems with ANY games (and believe me, I own a lot of games) apart from Crysis, Crysis Warhead and Crysis 2.
Anyone know of any way, apart from playing the game in a window?
I think the fix is vendor dependent (ATI vs nVidia). Both allow forcing the refresh rate, nVidia via its control panel, ATI by downloading Radeon Pro. I dont have 120hz though.