Heh, I actually had a one gallon tank for quite awhile... one of those cheap little kits from Petcetera (kinda like Petsmart for us Canadians) that had a really noisy air pump, small light, and an undergravel filter.
I put an Anubis Barteri nano in there (damn plant cost almost as much as the whole tank kit), 3 white cloud mountain minnows, and one ramshorn snail. They did pretty well, all in all. Of course, I had to replace 3 white cloud mountain minnows while cycling the tank (I didn't really know what I was doing... I had no water test kit for ammonia and no bio-spira or other cycling bacterial add-in). Once cycled tho, everyone seemed pretty happy, with regular water changes (stupidly easy in a one gallon tank... I actually got a tiny gravel cleaner... by the time the tube was full of water, I was almost done with the cleaning, heh).
Hardcore hobbyists might laugh with scorn, but ultimately it's what got me into the hobby, and the minnows and snail finally got a new home when I finally got myself an Eclipse6 tank. Add a bunch of new plants, 3 more minnows to complete the shoal, an otto, 3 cherry shrimp, and 2 honey gouramis, and I'm one happy hobbyist.