I recently ran across a forum thread in which the person who started the forum was documenting his construction of a 600 gallon saltwater aquarium.
My reaction is pretty much: WOW.
The documentation is quite impressive, starting with building the tank all the way to loading it up with an impressing (and expensive!) array of saltwater fish such as tangs, wrasses and the like.
This guy pretty much went all out. Props to him. I showed this to my girlfriend and told her that I planned on doing something similar one day (when I strike it rich somehow).
I would definitely recommend following the link and checking it out. You will be blown away.