Okay, after HOURS of research and elimination, I've narrowed down my list to four: Gonodactylaceus glabrous, Odontodactylus havanensis, Gonodactylus platysoma, and Gonodactylus smithii. They're all beautiful, interactive (to varying degrees), and play nice with others. The only one that isn't very hardy is O. havanensis. I'm going to keep one in my 29g. It's not set up yet, so I can aquascape as necessary. Thanks.