If you really, really want other cichlids with them, then look into blue rams, Mikrogeophagus rameriz(sp?0(same temp range as discus) and angelfish, Pterophyllum scalare (little lower temp, but people still keep them with discus with no problems). Good non-cichlids are chocolate gourami, cardinal tetras, kuhli loaches, and basically any other fish that isn't aggressive and can stand the temperatures discus require.
Male bettas are okay with adult discus... young discus might find themselves being chased. Female bettas will probably with both young and old.