need a tank size before you can get any GOOD recommendations on a fish. not too many people get a first tank big enough to keep some of the species already listed in this thread.
Depends on bullhead species, a 75 isn't good for any bullhead species that can reach more than 12". Yellows, blacks and browns easily surpassed 14" regularly even in capitivity and they are very messy eaters.I see you are also from Mass. (Me too.)
You obviously are referring to Bullhead cats, which are great for a 75, and will do well with cichlids, although when the catfish gets bigger, he MIGHT eat some of the smaller cichlids, but not usually.