When I was a young kiddie and the apple of my mother’s eye, I would spend part of my Saturday mornings watching Swap Shop on TV. Swap Shop was presented by British cheeky chappie Noel Edmonds and people would come on the show to swap their trading cards for a GI Joe, or their little brother in exchange for Yoda, and so on. Fast-forward twenty-five years and we now have more or less the same concept online.
NOTE: These sites are pre-dominantly US sites although it may be possible to register a non-US address. Check each site for details.