I have a 55 gallon tank also. Do you want a semi-aggressive tank or a community tank? The first fish I bought were tiger barbs not realizing they're fin nippers and mildly aggressive so I had to plan the tank around them. Little did I know for some reason they were dying and I kept replacing them but now I'm down to 3 barbs and will have to buy more since they do better in a larger school.
Currently in my tank I have 3 parrot cichlids, 3 tiger barbs, 6 giant danios, 3 (had 4) cory catfish and a pleco algae eater. I love my fish! Cichlids are smart and get excited when I go near the tank. It's like they wag their fins at me! They can be quite aggressive though. Oh and yes they all have names!
Here's a few pictures of my tank.
http://www.picturetrail.com/gallery....99&gid=6664427