Hi flyhockey1037
Ftbme is right, in a 2 gal you could have 1 maybe 2 Dwarf Puffers - Tetraodon travancoricus...in a 10 gal you could go with about 6 Dwarfs, or 2 South Americans - Colomesus asellus...in a 20 gal, maybe 10 Dwarfs, or 4 S/A's, or 1 Red Eye Puffer - Carinotetraodon lortedi.
One of the problems with housing puffers is that you can't go by the 1 inch of fish per gal of water guideline, they are generally very territorial and intolerant of tankmates, for example if you put 2 Red-eye puffers in a 20 gal tank, even though they only grow to about 2 or 3 inches, one would surely kill the other in a territory dispute.
No matter what type of puffer you chose to get, choosing tankmates is a gamble, some may work well for a while, but get chewed up as the puffers mature. You will need to be able to relocate tankmates at the first sign of trouble or you will lose them.
Some of the other FW species I've seen in the lfs are Target Puffer - Tetraodon leiurus, Pignose Puffer - Tetraodon suvattii , Fahaka Puffer - Tetraodon lineatus, and Avocado Puffers - Tetraodon cutcutia ...all very aggressive and best kept in a Species only tank.