+1 to Crysis,
Other good looking games to consider are:
Far Cry 2 (Graphics are nice but thats about it imo,Gameplay and story is crap)
GTA IV (Can look very nice maxed out) but you will need a very good machine with alot of graphics memory.
Batman Arkham AsylumAnother great looking game,Looks even better with High Physx Enabled!
Sniper:Ghost Warrior -Id actually say that the graphics in this game are similar to Crysis,although the story is not too good and the enemy AI is poor,The gameplay is fun though.
Bioshock-Ive only played about 1 hour of this game so far,Story is okay-ish,graphics are great.
Mafia 2-Considering this game is DX9 only,It looks amazing! and the storyline is very good.
Battlefield BC2 + Vietnam exp. -DX9,DX10 & 11 modes,Looks good no matter what DX you run it at imo.
DIRT 2 -Only played the demo,Looks very nice though in DX11
Out of all those mentioned,id recommend getting Mafia 2 first if you dont already have it.
So thats a few off the top me head,But you did not really say what type of games your looking for...Fps? Racing? Sim?