Cool Sequence Diagram Web Site
This is another of those really neat web-based tools for documenting your code: websequencediagrams.com. What a cool tool! This guy allows you to type in your transition diagram and then it'll render it for you in many different styles - including a very nice looking hand-drawn style. This is perfect for those times you need to whip up a simple sequence diagram and don't feel like all the mess and fuss of something like Visio.
Take a look. Pretty sweet.