The Python doctest module is really great: it makes it easy to simultaneously write test suites and demonstrate the usage for your modules. Python's interactive interpreter is key to its coolness: it's really easy to load the code you're working on, type some examples at the prompt, and turn the session into documentation and a test case.
I've been dusting off my Square Dance Revolution project, written in Java, and I thought: gee, it would be nice to use doctests here. A bit of inspiration from doctestj and Rhino, and a bit of elbow grease and: voila! JDoctest is born!
@doc.test tag, and you've got a test / use case example. I've added hooks to google-code-prettify to make the output beautiful, too.