I was recently looking for a great way to get Free Steam CD Keys to play my favorite games. I have figured out how to get these codes free is through Instagc.
You can sign up free and fill out free offers and then redeem the points for Steam gift cards in the amount of $20 and $50. The $20 card costs 2000 points and you can get that in a day if you work at your free offers.
I just redeemed my first $20 for my card, it was emailed to me to redeem. So simple. If you are looking for a free way to get Steam Wallet codes, these two sites are the best!