Nice looking tank, if it were mine I'd add a Gold Royal Pleco along with one or two SA cichlids, most likely a Severum and something else your into. Or, just to be a little different, maybe even a black ghost knife with the new cichlid.
Why not try a Paratilapia, although not CA or SA cichlid, very similar in personality, and are active, outgoing ,attractive fish. I had a small spots when I kept cichlids, and it was my favorite cichlid in that tank for 6 years that I had it.
How about some vieja species? I would stay away from black belts or Argentae as they can really be NASTY THOUGH. Some of the smaller viejas get some nice color on them.