There are a few popular types that you should be able to find at a LFS... Syno. Angelica, Decora, multipuntata, petricola, and if you are really lucky Brishardi To name a few of them. You could get an awesome school of peticolas going they would love to be in a tank like that. If you like the look of the plecos the Brishardi is the only catfish that i am aware of that has the sucker mouth like a pleco. They also have a really cool tubular body. PlanetCatfish has a bunch of pic/discriptions on these fish. Some of them (the ones that I mentioned for sure) are native to the rift lakes so they will handle the H2O parameters like champs. They would also give you some movement on the bottom of the tank, which I enjoy. Much perfered over Plecos in an african tank IMO.