I too am saving up for a bigger set up. I am keeping the 5 gallon with the critters it has, as they are a settled community and I don't think my betta would be happy if she wasn't the ruler of her little kingdom. ;)
I want a 2.5 gal quarentine tank, and the biggest set up I can afford (and that won't fall through the floor)! I want large schools of fish, in a fairly natural, carefully research and pre-planned community. (DormDrax is going to read this and laugh!)
This tank will be better planned out than most human communities, lol...
I have a lot of time to plan this, because right now both breadwinners in our household are unemployed... so for now, I plan my 'fantasy fish tank' and tend to the fishes I got.
The upside of all this waiting is by the time I can afford my fantasy, I will be a better 'fish mom' than I am now, and the fish will benefit from everything I am learning here...
Good luck on that 20 gallon tank!