I find it easiest to search at http://search.creativecommons.org/. It has options for searching Google and other photo repositories for open-source images including photos, etc.
Thanks, that'd be really useful for my blog.
Thanks, Rob, for another great find.
Unfortunately, the language Google uses to differentiate the images is not clear. For instance, which, if any, of those means "You may use this only if you pay a royalty"?