QueryTracker.net is awesome.
Everything a newbie writer could possibly need, all in one place! And all totally free! Create various personalized lists of agents and publishers, narrow your search to your specifications (for example: fiction-middle grade, agents accepting unsolicited queries) which makes this the most user friendly and easily maneuverable site I have come across so far.
Create lists of agents queried and keep track of the dates and their responses all with one click. You can also keep track of your actual query letter, which is quite helpful when experimenting with various letters as strategy. View statistics and reports about your queried agent-- how they reject, form letter or helpful, how many times they have requested pages, fulls, and the percentage of closed/ no responses from that agent. On the comments section fellow queriers can share their submission experiences and the response times for that agent. You gain valuable information about what kinds of projects that agent is interested in and has been taking on recently. All extremely valuable information.
QueryTracker.net is not just a useful tool for managing the query process, it is tool for sculpting and guiding the query process. QueryTracker.net is where I go first... and last