We found some nice 1-gallon pots of vincas, zinnias and celosias for $1.48 at Home Depot.
They also have large, patio-ready pentas, lantana and zinnias ($12.88) in terra-cotta colored pots that are a step up from the ugly, black plastic ones. They're still plastic, but the ribs give them texture.
I bought pentas a week ago and they still look great, though I have to water profusely to keep them from wilting. If you pick some up, be sure to offer filtered sun and afternoon protection until they get acclimated.