I've designed a couple of Keynote themes, and the biggest pain is that you can't start from scratch: you have to begin with an existing theme. The themes that come with Keynote are fine, but they have a lot of extra junk in them (e.g. wacky faux-granite image fills for shapes and charts, etc.) that will be tedious to remove before you can do anything useful.

The last time I made a new theme, I went looking for a "blank theme," hoping that someone had made one available as a starting point for new themes. No one had, and I was in a rush. Recently, I decided to make one, and I'm now making it available.

Blank.kth works with Keynote '08, features tasteful blue fills in charts, includes no goofy images, and defaults all text to Helvetica Neue. To install, unarchive the zip file and drag the .kth file to ~/Library/Application Support/iWork/Keynote/Themes/.

You are free to use Blank.kth for any purpose. Please let me know if you find it useful. Finally, I would appreciate -- but do not require -- that you share any derived themes with me.