List of agents, the site appears to be choosey about who they include - reputable agents only.
Agent Research & Evaluation News
Articles on agents and deals.
Agent Research & Evaluation Verification Service
You can check out an agent's reputation here - as well as sales he/she has made, things like that.
Association of Authors' Representatives
AAR is the professional trade group for agents in the US. The site has a membership list, and the AAR Code of Ethics is published on the site. Good to know.
Preditors & Editors
Online site listing evildoing agents and their schemes.
Free version - nice, but the subscription does provide so much more. For free, you get a daily email providing publishing news; once a week, the email gives you a listing of recent deals. Get the subscription from Publishers' Marketplace.
Great site. Deals in an organized manner, going back several years. Agents can be researched here. It may not have all the scoop, but it does have a lot.
Online version of the magazine. You have to subscribe. Expensive.
Science Fiction Writers' Association site that gives lots of info about agents, as well as publishers and the like. You don't have to be a science fiction writer to appreciate the great info here -- it's a great service that SFWA provides, akin to Preditors & Editors (see above).