Sarah, I would suggest you look up Tanganyikan shell-dwellers, neolamprologus multifasciatus (multis), neol. ocellatus or neol. brevis. These guys are fantastic to watch, you'll be an addict in no time.
Choose one of the above species, you can start off with 1m and 2f, which will need 6+ shells with an inch wide opening, sand or crushed coral substrate and a few rocks/cobbles at the back. Also see if you can get a synodontis petricola, they're beautiful and stay real small.
Read up on setting up a shell-dweller tank at the cichlidrecipe.com or lake-cichlid.co.uk