Yeah, quite a few. Although you do notice the quality of free games is generally lower than that of commercial retail games.
Need For Speed World, Combat Arms, Battleforge, Battlefield Play4Free, Battlefield Heroes, TAGAP (and soon TAGAP 2), and a few of the more professionally made flash games such as Ngame and Fancy Pants Adventures (though the latter is really only good for one or two playthroughs).
Spelunky isn't too bad, either.
EDIT: Oh, and how could I forget all the old-school freeware MS-DOS games that you can play in DOSBOX.