You can handle the i7-800s, the i5-600s and -700s, and the i3-500s.
I wouldn't advise getting the old i7s. They're just too expensive for their performance compared to Sandy Bridge. If you're spending that kind of money, you could get a new mobo and a 2500k or something.
The others are also comparatively expensive, but not enough to justify getting a new mobo.
How much power do you need, and what kind of budget do you have?