We have several subforums for such things -- Free/Donations, Items for Sale or Trade, and Members Only Thrift shop. Here's one of the FAQs, should answer most questions:
Guidelines for the Donations Forum (13 Nov 11)
There are some restrictions in those forums so that this remains more about discussion than commerce. I think most require you to submit your post to moderation first, and you have to have at least some prior activity on the board.