I have written a new jQuery plugin. It is a lightbox with focus on simplicity and usability. I call it kratsbox, and it's availiable on github. Instructions for use are in the readme at the github page.
I have used lightboxes such as fancybox and jquery-lightbox for a while, but havn't been happy with the keyboard usability of them (let alone the fact that they all seem to require image loading). Recently, Axbom linked to a specification for an Accessible Lightbox, which I agree with. After doing some more searching for a good lightbox, and still not finding any, I gave up and wrote my own.
Of course, I now use kratsbox on this site, so as a demo, here's some of my favorite images from 2011.