In addition to thier list (on both the website and in person) the following should be noted:
White Water Snacks in the GCH, Crocks Bits and Bites at DLH and the little Cafe (I foget the name) in the DLH near Goofy's Kitchen - 10% for all passholders - No Minimum Purchase required.
All other dining locations in the hotels, including snack bars and such - 10% for Premimum Pass Holders.
Also most places at DCA do not enforce the minimum purchase to get the discounts.