1. Smashing Magazine offers up a steady stream of stunning, free Wordpress themes. (see Resources below for some links). The site has an RSS feed, so you can keep an eye on the site for new Wordpress themes.
2. Free Wordpress Themes is another site offering free themes. They don't have as many as Smashing Magazine, but they may have just the one for you.
3. The Theme Lab offers free Wordpress themes and reviews them too. This site also offers general information about Wordpress and Wordpress plugins.
4. If one of your hopes for your blog is to make money using Google AdSense ads, wpSkins provides AdSense-ready templates for free.