I've had success keeping the following cichlids:
Discus (just recently, so my 'success' is limited), Angelfish, Apistogramma staecki, Neolampologus leleupi, N. brevis, Altolamprologus calvus, Julidochromis transcriptus, jaguars, oscars, rams, kribs, and convicts. All, I believe, are fairly easy as long as their needs are met; jaguars and oscars need big tanks, discus need warm water that gets at least weekly changes, and the Tangs need hard alkaline water with weekly water changes. Research is the key to success with any fish.
IME, HITH isn't caused by poor water quality and several sources I have read on it say that it may be a factor but studies are starting to show that the leading cause of HITH is mainly caused by poor diet. My experience on this is that diet it the leading cause... I used to have (before I knew better) 2 6'' oscars and a 7'' pleco in a 20g L and 3 4'' oscars in a 10g with 4 dwarf gourami and two 3'' plecos. I hardly ever did a water change and the oscars never got HITH; however, they did get quite a varied diet, feeder fish, flies, beetles, grasshoppers, crickets, worms, grubs, and hikari cichlid pellets. Of course, I know that this isn't conclusive evidence or scientific fact, just an observation and some research on my part.