You will quickly find that some agents make it easy to discover their likes and dislikes, while others prefer to remain shrouded in mystery. Here are a few of the sites that I found most helpful when researching and querying agents:
Literary Rambles Casey McCormick has assembled an invaluable collection of agent profiles and articles on querying.
Publisher’s Marketplace Not all deals are listed there, but it can give you a handle on what’s been selling recently and what genres an agent likes. I thought the small membership fee was worth it.
Agent Query Good articles (with a definite point-of-view) and good (if occasionally spotty) info on agent likes/dislikes and sales. There are other sites (like Query Tracker) that do the same thing, but I found AQ easiest to use.
Kristin Nelson Clear, vital information on query writing here. I also took Kristin’s science fiction and fantasy “webinar” through WritersDigest.com. The information was great and Kristin was very funny. The price included a pitch crit. (A bit controversial, I know, but I found it helpful. I got good notes from Kristin on my query and it gave me the courage to get out there and start submitting.)
Chuck Sambuchino’s Guide to Literary Agents
AbsoluteWrite.com These forums are loaded with information on agents, querying, contracts, and cautionary tales. Keep your wits about you.