Well, do you have a stand and hood/lids and lights for the tank? Bare minimum you'll need the tank, stand and lids for the tank...lights and/or a hood would make it look a bit more polished. To support fish you'll need a filter and at least one heater. I'd suggest getting a good canister filter (I have an eheim on my 55 and I really like it) and at least one heater. I'd probably opt either for one 200w, or to be safer probably two 100w heaters.
Other helpful things if you dont already own them would be: A
thermometer (either a digital one that you can get a reading from in the tank, or a suction cup one for inside the tank so you can monitor the temperature), a
test kit (with at least ammonia, nitrite and nitrate test kits), a couple of 2g
buckets (for "just in case" since you can't use household buckets for your fishtank), a
python (hose that attaches to a sink so you dont have to worry about lugging buckets whenever you do water changes),
dechlorinator (I hear good things about Prime, and I personally use big al's generic version of stress coat as my dechlor), good quality
fish food (I like OSI's cichlid flake for my cichlids)
Check
www.bigalsonline.com and
www.drsfostersmith.com for the best prices on equipment. I'd expect to pay somewhere around 15-20 for the heater and 80ish for a canister filter that fits your tank.
A lot of cichlids love sand, if you wanted to go that way, but I totally agree with having a darker more subdued substrate as it helps the fish feel more comfortable as well as showing them off a little more. With cichlids you probably dont want to just do one rock formation in the middle...you probably want to spread it out. They feel safer when they have lots of places to hide when startled or being chased.