The two commonly available kinds are the African Dwarf frog (ADF) and the African clawed frog (ACF). I suggest the dwarf frog. If you do a search on this site, you will come up with a LOT of info. I don't want to type it all out again (lazy I know, but I answer a lot of the frog questions). Here are some places to look:
http://allaboutfrogs.org/info/mypets/dwarfs.html
http://www.petfish.net/afrogs.htm
http://www.pipidae.net/david/ - i think this has some other frogs mentioned too
http://www.myfishtank.net/freshwaterprofiles.php?profile=124 - African Dwarf frog (that's my froggy

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http://www.myfishtank.net/freshwaterprofiles.php?profile=138 - African Clawed frog
You will NEED a tightly covered tank with filtration, a heater, lots of hiding spaces and not too bright lighting. I suggest nothing less than a 5g although I know a lot of people keep them successfully in smaller. I like 10gs. You can even keep them with a betta or something then. Feeding them is one of the hardest parts of keeping them, esp. if they are in with other fish because often times the fish eat their food. I suggest using a turkey baster or something similar and frozen bloodworms as a staple. They also like sinking shrimp pellets, chopped frozen baby krill and other similar things.
You can keep several ADF together - they are completely peaceful - to fish too. They can't be kept with any aggressive or nippy fish, however.
Make sure, no matter what you get, that you KNOW the difference between the ACF and ADF before you get one. They are almost identical when small. A quick rule of thumb is: if its front feet are webbed, its a DWARF frog. If NOT, its a CLAWED frog. The profiles I listed for the frogs shows the clawed frog's unwebbed front feet nicely.
I could go on, but if you have any other questions, just ask
