Tom, they're cool! How many do you have in the tank? What's the tank size? Any other fish in there besides puffies?? Have any of them puffed up yet? Can I ask you anymore questions?
cattlegrid_79, if you're looking for the scientific name I believe these are carinotetraodon travancoricus. The common name is dwarf puffers and they come in two varieties: carinotetraodon travancoricus and the less common carinotetraodon imitator. At least that's what I've read. They should grow to about 1". You can find more info here http://www.dwarfpuffers.com/
Tara, I have 3 in a 10g tank (pics of the whole tank are on my site). No other fish at the moment but I'm planning on adding three ottos soon and that will be it. No puff ups yet but since they only do that when threatened or otherwise stressed I'm hoping I don't ever see it