New ultra gamming rig. What great hardware intensive games have I missed?

Hey guys I've the pleasure of house sitting for a friend who has a $3000 custom build desktop and has given me the ok to go to town on his gaming comp.

I've been left to use my crappy laptop for the last few years so I've been relegated to the indie or other hardware unintensive games, keeping an eye on other titles but knowing I would never be able to run them.

So now I have this awesome computer at my disposal, where do I start?