Apart from the well known galleries, here are some free AJAX Galleries.
Zenphoto is an answer to lots of calls for an online gallery solution that just makes sense.
A combination of Suckerfish, Hoverbox and Lightbox to provide you with this impressive tabbed image gallery.
Simple Mouse-Over Gallery.
Thumnbails are listed inside a box at the left. You can click on the thumbnails to bring up a larger version in a right side panel. You can move between strip of thumbnails by clicking on left and right arrows.