Well, without knowing what you want to do with the tank I'm not sure what we can do to guide you in the right direction. Fish only tanks are quite different from reef tanks...soft coral are vastly different from SPS
corals. You aren't really giving us much to work with.
In terms of fish, you should check out the 'nano section' of liveaquaria. They do a really great job with how many gallons fish need to be healthy and thrive. Once you figure out what fish you can't live without, you can build up from there in terms of what it can live with and so on.