The number one problem I seem to have when faced with options for self-defense/martial arts is...which one do I choose? What exactly is the difference between Karate and Kung Fu? Which one best suits my goals/needs? Well, here are some sites that will explain the different types of martial arts to you.
Types of Martial Arts
This site gives you a quick overview of the different types of martial arts. It also has a directory to find martial arts schools in your state. The directory does not include ALL of the schools in your area, though.
Starting Martial Arts
This site lists the different types of martial arts by ethnicity. Some of them include links to more information about that particular form of martial art.
About.com: Martial Arts
This site, as most About.com sites, offers a variety of information on the topic of martial arts. I particularly enjoyed the articles "What are the Martial Arts Styles?" and "What is the Best Type of Martial Arts?"