Andy Ross, at Andy Ross Literary Agency, recommends checking out these sources:

Andy also has a terrific blog, which includes a feature called “Ask the Agent” with information about what a literary agent does and how to work with an agent.

Another option is subscribing to Publishers Marketplace ($25/month), which tracks deals, sales, reviews, agents, editors, and news.

HermansGuideYou might also pick up Jeff Herman’s Guide to Book Publishers, Editors and Literary Agents: Who They Are, What They Want, How to Win Them Over, an industry standard that is updated every year.