Working on finding one myself. The following site was recommended by the good folks at National Novel Writing Month. It is FREE and bills itself as the largest and most current database of agents. Here it is: Agent Query. I have been impressed with its ease of use and the updated info, plus its search function.
I would not recommend wasting money on the annual hardback of Writer's Market. It's much better, IMO, to pay an annual fee of $29.99 to use their online version at Writer's Market. The online version has a myriad of search parameters, a personal file where you can track your submissions, save listings in file folders, etc. MUCH easier to use than the book AND it updated throughout the year. IT si well worth imo.