Steam occasionally gives its users guest passes for their games. I have one for TF2. It's good until 9/20. Just leave a post with some witty Half-Life or TF humor in it... I'll pick a random CAG tomorrow when I get home from work.
If no one asks for this, I believe I saw someone on the "Ask For Free Stuff" thread in the Video Game Trading category. If he didn't get it yet, I'll sign up for him.