BFBC2, Crysis, GTAIV and Prototype are games I know to require fairly significant CPU power to get high framerates. I've heard Black Ops takes a fair amount as well but don't 'know it' for a fact.
BFBC2 is definitely the 'biggie' ATM. It doesn't help that it also has GPU usage issues when you play it online.
However, when you have a CPU BN, it means that you should turn up the settings more on the gfx card. You might as well, right?