I've seen how-to videos for making wallets out of old playing cards or out of their boxes. Another interesting idea is laying them out on a table and covering the top with a sheet of glass. Some bars have done similar, but they shellacked the cards to the bar surface.
Using them for magic tricks which involve destroying cards is a good way to go. If the deck is worn but still intact, handing them down to a little kid to play with works fine - they don't care about fanning and glide when playing Go Fish or Crazy 8s.
