I had initially been thinking I would get 2-3 puffers for a 20 gallon, but I just felt I couldn't reliably sex them at the pet store, so I decided to go with just one for a 5.5 gallon
Here's his tank currently. I am still waiting on some plants to get shipped (in the meantime I have thrown in some cuttings from another tank, to make the tank more jungly than you see in this pic)
here's the little guy:
And a video
not sure how to embed the video?
http://youtu.be/pcDOL_vrLpk