My critique group has been discussing agents and queries a lot lately. We're all gearing up for the agent-hunt. I've got a list of about ten prospects so far. There are so many great resources for the search, but it can take serious time away from writing, revising, and critiquing.
I've been using:
1. Literary Rambles (Casey McCormick) - Casey has great list of agent profiles, as well as questions to ask when you "get the call."
2. Query Tracker - great way to organize your lists as well as basic information about agents.
3. Various agent blogs - if you're not aware of it, many agents blog and tweet. It's a great way to get a feel for who you might want to query.
The most important tip I've seen lately is this: Follow the guidelines. FOLLOW THE GUIDELINES. And every agent has a slightly different version. Make sure you read the fine print. Don't get yourself booted 'cause you didn't follow the rules.
But first, finish the book!