Go to the public library. This information changes so frequently (who is representing whom) that it goes out of date quickly. I'd be highly suspicious of a free source being up-to-date.
Echoing Knightly's comments, if you're expecting to profit you need to be respectful of the people who expect to profit from their efforts.
If you are simply looking to find literary agents, there are a few sources out there. The Writers Guild of America (WGA) provides a free listing with contact information. I should point out that these agencies are VERY HARD to get a consideration if you have no credits. If you are looking for representation, some avenues are Inktip, contests (though I'm loathe to recommend these as there are so many scams), and workshops. Professional workshops and classes are often a convenient in for promising scriptwriters. In all cases, be expected to put in the time and effort. Despite living in a digital world, many agencies still prefer print copies for their readers. Unless you're established, expect that you're going to receive a number of rejections. Even with credits, you need to expect that your script may not meet the studio/producer's needs. Some of the start-up production companies will often put out an open call for scripts. In all, be careful and protect your work. Many contests and calls for scripts simply take your money and ideas with no return.
As Rayw is often fond of pointing out, there are lots of scripts written and very few movies made. Given that, it is often better to produce your own script(s) to build up some credit before seeking out representation. From their perspective, they make money building on success, not the unknown. It's hard breaking in as a new novelist trying to get an agent or publisher to consider their masterpiece. It's a zillion times harder as a screenwriter if you don't have contacts or credit.
Probably not the answer you sought but hopefully advice you can consider. Good luck.