Some of my querying links.
Query Tracker: Database of agents with response times and filters. I keep a list of agents queried, along with responses. Small annual fee.
Absolute Write Forums / Share Your Work / Query Letter Hell: A writer forum with the chance to get feedback on your query letter from other writers. Put in your homework here and you’ll be able to write a passable query letter.
Twitter / #mswl fantasy: If you don’t know about #mswl, it’s short for Manuscript Wishlist, and agents and editors will put this on tweets to get author attention. If you’re querying a novel with those characteristics, they want to see it. Obviously, if you don’t write fantasy, use a different search phrase after #mswl.
Manuscript Wishlist: Likewise, this website catalogs agents and their specific requests (along with general areas of interest).