In fact, I think I'll list my favorite three of these type of pages first:
Preditors & Editors
The Rumor Mill
Agent Research - a good sight, will tell you some things for free, but for a full report you'll have to pay money. (hence, a very nice place, but not my favorite. :D )
Fiction Addiction has one of the best agent lists - AAR approved and not.
All About Literary Agents
Association of Author's Representatives Homepage
Authorlink Agent Directory
Guide to Literary Agents
Lady K'Lyssia's own agent hunt:
Literary Agency, publishers, authors, conferences, query letters.
Literary Agent Homepages
Partial List of Fantasy Agents
Romantic Times - Romantic (genre) Agents
The Author's Registry