There are several types of stretching. The two main types are dynamic stretching and static stretching. Static stretching can be further subdivided into active and passive. Passive means using some outside force to hold the stretch (e.g. a chair), whereas active means using your own muscles to hold the position.

Here are some good dynamic stretching references:

From the Sports Fitness Advisor

Here are some good static stretching references:

From the Sports Fitness Advisor