Petsmart sells a very nice plastic rock. It's expensive ($47) and hard to find. It's labeled as X-Large (~20" long, ~ 14" high, ~ 6in wide. I have one in my 75G and 150G African Cichlid tanks. Lots of holes (caves) inside, and the bottom provides two large caves. The rock looks so real I use it as my center piece for my 150G Tall tank.
I would shy away from driftwood in an African tank as driftwood does have a tendancy to release something in the water that I can't remember exactly what it's called, doesn't hurt the fish or anything but it does drop the PH levels in the tank which africans frown upon since they prefer PH levels higher up in the 8 range or so, maybe a small piece here and there but if you use it keep a good eye on your PH levels
It's the tannic acid. Turns water soft and semi brown in color. I use to have a lot of drift wood in my planted tank. Tool them out because I needed more area for sword plants (Echinodorus).