5 gal
Hey tankgirl, any ideas yet...? I'll spit out a bunch of ideas but I doubt you'd be interested in any of them...
crayfish, water bugs(i've kept them before), a leech(they're fun to watch), firebelly newt, you could breed live food...
toads, salamanders, a small snake(there are a few that would be ok in a tank that small), millipedes
, pill bugs, sow bugs, scorpion, spider...
Well, those are some of the things that I have kept in the past that I had fun with... Just thought I'd throw a few more options out there... If you ever to cross over into the creepy crawly side of pets then make sure to check out
www.reptileadvice.com
If you insist on sticking to aquariums and you had any interest, a tank with different types of water insects can be fun to watch... many different types of water beetles, dragonfly nymphs, and quite a few other little critters... I find them pretty interesting to watch...