Hi Erin,
stuff I've experienced with cichlids....
Kribs aren't -that- aggressive, I've had a couple spawn twice in a 10 litre tank, I eventually chucked 'em in with my 200 litre trop set-up and unfortunately the male died, but the female used to hang out with an old cacuatoides (dwarf cockatoo) and now that her spawn are getting large enough she's courting one of her spawn (a bit wrong, I know, but what can you do? they're territorial but I've got em in with bristlenoses, and even neons/bloodfin tetras, and as long as everyone stays away from their nest everyones' been cool, I dunno, I've had a few kribs over my time and they can be picky, and if they're not a good match for each other they will fight to the death, but usually they just leave other fish types alone/chase and defend their territory.
in the shop I worked at we minded a big tanganyikan set up full of tropheus, these guys are great, if you have enough of them there is no real problems with picking. the guy had all these huge golden chinese algae eaters (the ones that are a real no-no with goldies) when these guys are big enough they're aggressive/fast enough and can stand the hardness of an african cichlid set up. -They also look WAY cool when they're bigger! (7-8inches)
if you're wanting a proper biotope cat for your tank you could try a synodontis cat.
if you're wanting African, there are two regions, (well three, but two main ones) Lake Malawi and Lake Tanganyikan. In general, Malawi have the more brightly coloured fish, and Tanganyikan have more diverse mating rituals.... I prefer the Lake T. ones, just because of the variety. shell spawners, substrate spawners, mouth brooders etc. so much fun. If I was to set up a tank I would want some altolamprologous calvus or comprecciceps coz of their cool shape, and also coz these guy are relatively peaceful as far as cichlids go, my dream tank would be to close off all the holes in my house, fill it with water and have a whole heap of C. Furcifer swimming around, these guys are spectacular looking fish, but unfortunately need space..
When I got back in to fish husbandry a few years ago after a period without fish, I was originally going to get into cichlids in a big way. I did a whole heap of research and watched a lot of their behavior at work, but I refounded my love of the humble goldy and have dedicated myself to them now!

I'm a passive sort of person, so I decided keeping aggressive fish was not really my style. goldies are such gentle old souls... but I digress..
Cichlids are cool!