Auction them on e-Bay then donate the money to a charity... Methinks that baseball cards dontated to the United Way, et. al, will sell for far less than they would sell for on e-Bay, thus giving the charity less money (not to mention overhead costs for selling those cards which I imagine are higher than having someone open an envelope with a check in it).
Card trading on e-Bay is very lucrative. Friend of mine quit his day job as a jet mechanic just to buy and sell cards on e-Bay all day long. He makes enough money to support his family and bought an M3 a couple months back (used, but still cost in the 30k range).. You should be able to make enough money to make a nice donation to a charity of your choice..