Toribash
uhmm... i like those m.u.g.e.n. games, they're kind of 2d beat 'em up meets dragonball, meets naruto, meets one piece, meets bleach, well, meets any kind of anime chars, and more! Just download a mugen game (search @ google: M.U.G.E.N.) and try downloading all sorts of fighters, like popeye superman, batman, anime fighters and so on! And of course, it's 100% FREE!

Here the links: M.U.G.E.N. game: http://mugen.en.softonic.com/ (just click free download )
M.U.G.E.N. chars stages and so on: just search, there are !!loads!! of them! ;P
Look, here's your mama! I'm TheOnlyOneWhoDoesn'tHaveAFoxAvvy, haha!
F.E.A.R multiplayer

completely free, download it and get your key-code from projectorigin.warnerbros.com
If you get a Steam account (which is free), you can get Half-Life 2 Deathmatch, Trackmania Nations Forever and a few other little games like Peggle or a Sam and Max episode for free.

There's also about 15 games on sale for under a dollar right now. Don't you love the holidays?