Good looking is relative. Perhaps if you better defined the type of fish you like. If you want flashy color probably a cichlid like shen... said. I'm not that into cichlids myself. All the really impressive ones that I might consider keeping require huge tanks. I did considered a green terror for my 55 for a while. In general I like more natural colors. Quick testimonial - I just set up my 55g again, and after keeping solely chacarins for years I wanted something different and did a lot of research. I decided on keeping a bichir and building a tank around keeping a few of them. I have a Senegal now and so far I love him. At only 2" hes fascinating to watch. He's very active always exploring. He attacks food very aggressively, and death rolls earthworms. They can be kept with other fish as long as the other fish doesn't fit in their mouth they'll ignore it. They also live well with others of their own species. Again
'good looking' is relative, if you like the odd looking things, I suggest you take a look through the poly forums and consider a bichir.
