WordPress 1.5.2 has some fairly rudimentary quicktags for things like bold and italic text.
… But I saw the plugins page, and wondered “What’s Textile?”…. So I headed on over to the author’s page, and discovered that it lets me use underscores and asterisks to achieve _italic_ and *bold* text.

Oh frabjous joy! It’s Almost Like Twiki! [/me takes cold shower – readers who know me know my fondness for this particular wiki]

I wonder if there’s a full-on Twiki markup plugin?