Sebastian Brink developed a prototype based, easy to use, fully customizable image Gallery called “qGallery”. You can change the look and the size of the Gallery with pure CSS settings.
It’s really simple to use, you just have to include the scripts into your page and insert a simple div at the position where the Gallery should appear. You can upload your images in full resolution, every image processing is done by some php scripts on the server. To define image sets you just have to edit really simple XML files.