I thought a good book to get is "Success with an Amphibian Pet" Poison Dart Frogs - By William Samples & Jack Wattley. They give a good description of basic husbandtry of many kept species as well as some basic breeding and medical information. Go's for about $20 at Amazon.com
Jewels of the Rain Forrest is a nice book for refference to different species with excellent photo's although it's a bit pricy and doesn't give much info on keeping them in captivity. I got my copy used for $65.00 from Amazon.com.
Also, the British Dendrobatid Group's web site has some good info as well as the others listed in previous posts.