i'm not sure if this will be a DIYer, and i'm a big newbie to fish so maybe my idea wont work, but i thought this tank that i have built in my head would be absolutely awesome when i get my own place (since apartment renters don't exactly like huge fish tanks).
basically, imagine a ten gallon tank... thats not much. ok now, extend the length so that it runs along two walls in the room, and it can sit on custom cabinents. can you picture it? basically it follows the wall, turns when there is a corner and finishes at the next corner.
of course, once installed, the only way to get it out would be to destroy it... and lighting/filtration would probably be horrendous, but i think it would be worth it.
i'd put a couple different schools of cory cats (my favorite) along with other fishes that don't need tall tanks. and i also figured that the terrain in the tank could vary from open to "forest-like" and other various habitats, and maybe create little cities using different themed decorations in different places... (like create a china area, and then a bayou/new orleans area, and maybe a caribbean area...) it would probably take forever to set up.
i dunno... maybe i am just crazy. i've only had a tank for 6 months now, but i absolutely love it. i'm always reading about fish stuff and i think my college buddies are starting to question my sanity, especially my roommates.