While keeping in mind that Discus ARE cichlids, they cannot be kept with many of them. Most Cichlids are agressive, territorial, etc. Therefore, you will need to find a peaceful cichlid that will go with Discus. Although some of the African cichlids may be very colorful and nice looking, they are unacceptable tankmates for Discus. The larger South American Cichlids are also unacceptable to be kept with Discus. Below are some choices of Cichlids to be kept with your Discus
Rams - Rams are very colorful, and above are the German blue Rams. There are also Golden Rams which I keep.Vey colorful and peaceful. Grow to about 2.5".
Festivums - Very cool fish. I used to keep these, and this is a picture of one of mine. Might only want one per tank, aggressive toward other Festivums. Grow to about 6"
Keyholes - Really neat fish, look similar to the Festivums, but are a bit smaller. Only grow to 3" and are also peaceful.
Uarus - Related to the Discus, somehow. Breeding is the same with the mucus feeding on the side of the fish. Not aggressive, but grow huge, 12". Almost every time I have seen one of these in a any store they have diseases.
Angelfish - One of the most popular aquarium fish. Some say that Discus cannot be kept with them, but I beg to differ. They are fine tankmates, and live in the wild together. Grow to about 5 - 6" depending on the species.
Dwarf Cichlids - Pretty good variety, so you can pretty much pick out what you want, just make sure that they aren't aggressive, and watch them carefully after they are put into the tank. I call them "Napoleons", small but can still kick some ass.