http://www.lizadawsonassociates.com/faqs.html The FAQ has some great info about queries & other general questions
http://www.knightagency.net/ Two places I enjoy on their website – the Manuscript Submissions page and at the very bottom, you will find several links for approaching an agent, what to look for, writing a query, FAQ, etc. They also have a newsletter and while that is filled with their authors’ interview, new books, they also have an agent roundtable, and the watercooler that is good to keep an eye on.