I know they are often over looked a lot by most people but garter snakes make awesome display animals. They come in a huge variety of species, subspecies, colors, and morphs. They are extremely active too, they don't hide all day like a ball python. they are pretty interactive too and don't mind being in small snakes, probably the most social of all snakes.

I have a black x grey x yellow rat snake cross that is an awesome display animal, no crzy colors but he's interesting. He's out all crawling and climbing most of the time or basking and they get a decent size. So any of the American Rat Snake subspecies could work.