UnGallery has finally moved to a 1.x release status with the addition of plugin Administration menu.
UnGallery displays directories of images as a browsable WordPress gallery.
The advantage of UnGallery is there is there is no gallery management required in WordPress. You just point the plugin to a directory of photos, even thousands of them organized into sub-directories, and they are immediately viewable via an existing WordPress site. Any uploads, deletions, or edits you make to your photos and directories are automatically reflected in WordPress.