Malawi mbuna or peacocks would be the best choices for size/color in a 125. You can fit more mbuna than peacocks, but mixing them is a bit more difficult. Peacocks aren't as diversified in their habitat choices and/or aggression levels as mbuna. Definitely best to stock one type of fish though, and forget about mixing SA or CA
cichlids with African rift lake species.
Check out cichlid-forum.com and spend some time reading some of the various posts regarding mixing different species. Pretty much any posible combination will be found/discussed there, and you can save yourself quite a bit of trouble (and $$) by researching thoroughly.