This isn't a super cute project, but i thought i'd post it incase there's someone out in cyber land that needed an idea for a fishtank...
I redecorated my room last summer, and i really needed some kind of a vanity. We had this old nasty fish tank lying around, and it was a great size. I used a ton of nasty chemicals to strip the rust/paint off, painted it white, and just got two pieces of glass to use as surfaces. It probably cost a total of $10!
I also think it would be pretty cool to just leave the tank in the base, and put a piece of glass over that... just fill the tank up with funky toys, etc.