Site: http://www.tf2wh.comThis is the usual trading service for TF2 items, but here is the cool thing!
http://www.tf2whx.comThey have created a dedicated exchanger for credits of the first!
So you will be able to use Bitcoin to buy credits, and then buy TF2 items with these credits.
But you can also simply trade your TF2 items for credits, then convert them to Bitcoin and withdraw to your wallet
I'm not the admin of this service.