Tip: A Really Good Book About Agents

The best book I've found on what agents really do, what to expect from them, how the agent/client relationship actually works, how to assess an agent's quality, how to tell if they are reputable or scamsters, etc., is Literary Agents: A Writer's Guide by Debbie Mayer. It's a little older than some of the stuff out there, so you might need to get it used, which you can do on Amazon (here's the direct link: Amazon.com: Books: Literary Agents: A Writer's Guide) or A Libris (here's that link: Alibris - Used, New and Hard-to-find Books, Music and Movies).

The book also has some agent listings in the back, which I did use in my first mass mailing. However, it's not that large a section, and for mass-mailing of queries purposes, you're probably better off with the latest edition of a Writer's Market.

As always, good, good, good luck!