It depends on the place. The only one I can remember offhand is Cosmic Ray's - we had a choice of chocolate or carrot cake. They were single servings in a little cup, not slices off a larger cake. Oh, I think that Pop's food court allowed us to choose between a lot of their dessert offerings.
Check out allearsnet.com for some more ideas. There are probably cookies and brownies and cheesecake and such at a lot of places....