I found this new site, where you can order trading cards, wallet codes, and steam games for playing achievement games, completing tasks/offers, watching videos. I've already ordered 9 TF2 cards and Super Meat Boy. If anyone wants to try it out, you can register here: Tremor Games - Play Achievement Games, High Score Games | Win Gifts and Prizes
Please let me know if it works for you too. Good luck! :D