So, not so long ago, I found this website, Goozex. Basically, its a website to trade games. It works with points. You can buy the points or trade some games you already have to get some. But until june 30th, you get 100 points when you register on the website. With 100 points I had enough to get something like, Command & Conquer Generals ( with the expantion ). There are also tons of other classics and not so old games like Warhammer 40k or nice stuff on the gamecube, ps2, xbox etc. Also, you get another 100 points for the first game you receive. When you receive a game, you have to send a feedback to the website ( theres a small button under the game you selected on the website for this, it takes like 20 seconds ) In your feedback, you tell them if the game works well and if everything is all right. If the game is broken, scratched, or doesnt work, they give you back your points. Its pretty nice, I just got my 4th game from that website. Try it out! Just as a reminder, its COMPLETELY free until you decide to pay for your points. NO hidden fees heres the link http://www.goozex.com/trading/asp/join.asp?idr=578534236619
Makes me think of barterbee.com. Except barter bee is with anything not just games. I've never tried it myself so I can't say much more about it.
Well from what I've seen so far I think you should try. I got nice games like Quake 4 without paying anything