Okay, when this gets going, I'm in! I have six sets waiting to be decorated, so this is perfect because it will get me going on them! I like the idea of animal-themed ones but, as much fun as double entendres are, I don't think I could come up with any clever ones
Some other ideas, maybe:
sports (either types of sports or sports teams)
But I really like the animal idea the best (followed by food)!
ETA: I just thought of another idea... Holiday themed?