With the recent changes in Facebook Groups, some dormant groups have become quite vibrant and active recently. One that has already proven to put me in the "duh, WINNING" category is the "Baseball Card trading, buying, and selling" Group.
First and foremost, bear in mind that unlike many trading forums around the Web, this one is sort of "wild wild West" when it comes to lack of rules and regulations. The wheeling and dealing here is un-policed for the time being, and for now neither Facebook nor the group admin probably have any intention of putting any regulations in place. So, as with anything done online, caveat emptor.
Having said that, it is proving to be a pretty good place for acquiring cards for resell for me at either eBay or Checkoutmycards.com, including 2011 Orlando Cepeda and Joe Morgan patch cards from a Cleveland Indians collector that only cost me Travis Hafner and Kerry Wood relic cards.
Good luck with this new place for completing a wish list, helping someone complete theirs, turning a profit via resell, etc.! There's only 94 active members at the moment. Let's grow it and make it a win/win for everyone.