convict,firemouth,jack dempsey,festivum,nicaraguans,sajicas i would not ever put a severum in a 55 gallon after seeing with my own eyes at a pet store this green severum almost a foot and cramped in a 55. The list above is for a few but not all.
if you get a jack watch for ones that might have an attitude problem. my female did and killed off my oscar and almost the other one too
im new to larger cichlids also, but you can get a firemouth (as mentioned) and maybe 1 or 2 geophagus.
geophagus are not aggressive at all so get them full grown or at least bigger than the other fish. some of geophagus have lame colors but some of them can get bright.