Don't know if you care, but I'd use it for a Loach tank...
I got 3 Clown loaches that are 8-9" and another 4 that are over 5"... I always thought it would be cool to do a driftwood/river tank with huge loaches and such...
Just my idea of something to do with it.
do you want predatorial fishes or just simple nice ones?
not to offend anyone in this forum but if you do... only if you do... have some spare $$$ you can start with dats. you need to give us a budget... for some $500 is small for some it's big.
if i had the space for one more 180 gal i would do a planted tank with angle fishes, neon tetras, corydoras, and some nice colorful loaches... one more thing is to get some exotic pleco after you have saves some more $$$. its more of a variety of semi-agressive to peaceful fishes.