Here's my Markdown. It's great to be able to write in (nearly) plain English - say, for submitting something for print - and being able to dump the same text down into the blog and have it work on the web. Setting aside writing-for-web vs. writing-for-print issues, I find this a great help.
And PHP Markdown Extra adds a few niceties, like Markdown inside HTML block tags, simple tables, and definition lists. It just drops straight into WordPress and away you go.
For more information on Markdow (or it's use in PHP), you can check out the Markdown manual first and the PHP one to follow up...
