Understand the themes and genre of your script. Some agents or producers work specifically with certain genres or types of material.
Make a list of people, either through directory books, IMDBPro or Craigslist that fit the material you wrote.
Research each to find out their policies on unsolicited material. This refers to scripts from random, yet-to-be established writers.
Producers are more open than agents to unsolicited queries, so you may find more success talking to them as a start.
Send them your script with a one-page synopsis as well, and a bit about yourself.
If the agents accept unsolicited queries, they will have instructions for you to follow with regards to your submission. Don't overdo what they ask.
If you get "in" with a producer first, ask him to act as a conduit or referral to agents to help you get your foot in.