Gallery Widget Pro (gallery-widget-pro) free WordPress plugin

A widget that displays rotating images from a post’s gallery in the sidebar of
your site. You just specify the post or page, and it will cycle through all the
images from the gallery of that post or page. you can have as many of them as
you want on your site simultaneously. Requires PHP5.

In WordPress 2.6, another plugin of mine has been included into the CORE to
allow these to be reorder your images to make them display in whatever order you
prefer. Until then, go get Reorder Gallery!