If you really like your cichlids. I'de go for a pair of something bigger and more "uncommon" take the proverbial plunge and get something nice. or look into the Pike cichlid Species.
silver arrowanas and rays would be okay for awhile but you'de deffinately need something bigger in a year or so.
Poly's are a fun lot. never thought I'de get as much as I have into my guys. and they would make a nice bottomdweller in a med-sized set-up. they'll eat anything small enough to fit into their mouths but tend to leave other tank-mates alone otherwise.
i will get dimensions soon. (The tanks outside filled because im checking for leaks) plus its storming & thundering outside. I will get them as soon as possible. Plus guys this will be in my basement which is were we always hang out ( Indoor movie theater) So we'd like the fish to be colorful and, um spontaneous is what i think my dad said.