Hofsinzer's All Backs is one of my favorite tricks to perform that requires a double backed card.
Michael Ammar does a great performance of it: https://www.youtube.com/watch?v=pa6fc_pDKDM
The Anniversary Waltz also requires a double back card, and that's an absolutely fantastic trick. Also requires a double face card, however. This is one of those tricks that a spectator will remember forever if you present it well. (I use Oz Pearlman's True Love presentation.) https://www.youtube.com/watch?v=4GPs3iUIHn0