Lightbox 2
Lightbox is a simple, unobtrusive script used to overlay images on the current page. It's a snap to setup and works on all modern browsers.
fGallery
WordPress image gallery plugin which seamlessly intergrates with WordPress. Administration page for uploading files and managing galleries integrated in the WordPress administration area. Supports gif, jpg and png images. Integrates lightbox right in the plugin.
NextGEN
NextGEN Gallery is a full integrated Image Gallery plugin for WordPress with a Flash slideshow option.
WPG2
WPG2 is a Wordpress Plug-in that embeds Gallery2 within Wordpress to share photos, videos and any other Gallery2 content seamlessly into the Wordpress Sidebar and Blog entries.