The folks at FooPlugins have announced a free version of their FooBox lightbox plugin. FooBox has been under active development for about two years, which is saying something in the world of lightboxes, where many free jQuery driven options have gone by the wayside.
The free version of FooBox handles just images, which for many people is all they need. If you want all the features of the commercial version, including support of other media types, you can upgrade for $27.