At my school (k-8) one teacher teaches 8th grade, and 7th grade science/P.E (I get the strangest sense I'm his favorite student...)
I told him that he should setup a fish tank in his room, and he asked if I would be willing to do maintanence. A few minutes later, it was decided that he'd get an aqaurium. I have to bring it home summer/long vacations and do maintanence, and when I graduate the tank is mine! The school has a lot of funds so they're paying.
Not exactly sure what size it's going to be, but 5-10 gallons fits best on the place where he wants to put it. SO, it'll be probably a 10 gallon tank with maybe 3 albino cories, 5 neon tetras, and a Betta. That... or maybe setup a sorority with pygmies (This is a school full of kids with short attention spans, I can't have one type of fish or they'll ignore the tank and it's purpose to the teacher, which is to make people more peaceful and focused, won't work.)
So, in a year, I'll get a free 10 gallon setup! And in the meantime, I can keep the fish healthy and happy!