This plugin by The HungryCoder will rotate the header images on the Twenty Ten default theme that ships with WordPress 3.0.
wenty Ten comes with a selection of header images. It’s easy to switch between any of the included header images or upload your own.
Twenty Ten neatly organizes your pages into a menu right in your blog’s header, and includes drop-down menus for multiple levels of nested sub-pages.
Twenty Ten includes special styles for posts that you file in the “Asides” or “Gallery” categories
Theme demo: http://2010dev.wordpress.com/
Plugin homepage: http://hungrycoder.xenexbd.com/scripts/header-image-rotator-for-twenty-ten-theme-of-wordpress-3-0.html