the synos are always a great choice but will want different water than u'r flowerhorn. smaller bullheads are always good too. the pimelodella blochii (4 line) will get a lil big for the 90 as i've seen up to 16-18" personally. could always do some banjos, cories, or raphaels like wyldfya mentioned too, they would work good as long as the cichlids wouldn't be too agressive. but my personal fav would be some pimelodella gracillis (single line pictus) or a small pack of ompoks (sweet lesser known cats). in any case good luck