I have universally been told that a phone call is the most effective way to communicate with your representatives. I have no sources to cite, but this is based on conversations with my representatives' staffers as well as door-to-door petition-type people.

Anyway, here's the link to find your rep: http://www.house.gov/representatives/find/

Side note: if you're ever going to Washington D.C., you can make an appointment to meet them. They aren't always available, but they will typically at least have a staffer give you a tour of the capitol, which is pretty sweet.