what to go with Butterfly bush. . .

I have a half-circle (about 9 ft radius) bed with a (very young) chinese elm tree and two small (for now) butterfly bushes. This area tends to be wet in the fall and spring, but normal moisture during winter and summer. Any planting ideas? It's in pretty much full sun all day. I'm tired of the bare spots, but I've had problems with plants "melting" from the wetness. I would preferably like something colorful. Help!