LOL you just knock me out. You've got tanks and never know what to put in them! My problem is the opposite -- I want too many fish and have to get more tanks for them.
As I told you a while back, I have a 20 long I'm going to do little puffers in (have decided to go FW puffers). I'm going to dig it out of the shed, clean it up, and start cycling it this weekend, so that's exciting.
As for what you could do with your 20's, I'm thinking here...
Do you have access to Exodons? You seem to like them... why not do a school of those?
How about a small Amazon community tank? Tetras, Hatchets, Corys, maybe an Angelfish... I've got one of these, except it's a 125, and I really, really like it. Lots of action all over the tank.
Have you ever heard of halfbeaks? They're a really interesting-looking livebearer -- look sorta like a gar or the gar-ry characins. Might be neat to breed them.
That's all I've got off of the top of my head. Try looking at this page:
http://www.wetwebmedia.com/ca/volume_5/volume_5_3/stocking.htm
It's got lots of ideas for stocking smaller tanks/