Rams are nice, I keep mine with panda cories and cardinal tetras. With a 55 you have lots of options, I just looked up penguin tetras and they look pretty cool. You could easily do two pairs of rams, and a couple good sized schools of something. I would stick with tetras with rams. I've read on a few sites that tetras are best de to thier tendency to be a little more mellow, danios are hyper and it's said they stress the rams as a result, something to look into (I don't really know anything about them) galaxy rasboras look awesome but I don't know thier temperament.