Aaron D. Campbell

Gives you the ability to simply drag and drop to reorganize your images how you 
want them to appear in your gallery. If drag and drop isn’t your thing, it also 
adds an “Order” field to the images in your gallery, much like pages have, which 
allows you to reorder them to display in whatever order you want. Requires PHP5.
If you are having problems sorting since version 1.0.1 of this plugin, read this:
In order to fix another bug, I had to use the filename as a “handle” to drag by. 
When you move your cursor over the name of the file, it should change to a 
“move” cursor, at which time you can drag/drop the image as before.

Reorder Gallery

Allows you to reorder your gallery images with the ease of drag and drop. Resquires PHP5.

Magda Sicknick

The plugin allows users to turn on taxonomies they would like to order and drag and drop to a desired position.

Reorder Gallery vs Custom Taxonomy Order