Is there a way to exchange games with people?

Hey guys, so I have coupons for the following games to get them for free (via steam I believe): Far Cry 3, Bioshock Infinite, and Tomb Raider. None of these games really interest me (plus I already have Far Cry 3), and I was looking into buying Starcraft 2.

I am just wondering if there is a legitimate site where I could see if anyone was willing to exchange a brand new SC2 key/game in exchange for these 3 games that I have. Is there anything out there like that?

You can try here http://www.steamtrades.com/forum or the steam forums.

EDIT: I'll buy Far Cry 3 if your interested. $20 on paypayl.

At what price? I'd like to see if I can exchange it for StarCraft 2 first.