Herper.com Blog
Salamanders - Caecilians
Frogs & Toads
Treefrogs
Poison arrow
Mantellas
Horned frogs
Ranids
Clawed frogs
Other frogs
Toads
Strange Batrachians

Xenopus (African clawed frogs) are commonly used in the scientific community for research purposes, but they also have a large following among amphibian hobbyists. Other pipids, like Suriname toads and dwarf frogs, are also available occasionally.

Pipidae links:

Herpetological publication links (PDF):

Lobos & Measey. 2002. Invasive populations of Xenopus laevis (Daudin) in Chile. Herp. Journal 12: 163-8.