I’ve been a user of Lightbox for years. It’s an amazing step forward in usability for websites, a beautiful way to display modular information without annoying pop-ups. Recently two new frameworks have come to my attention.
Slimbox is a Lightbox compatible framework that is MUCH smaller than the slightly large Lightbox framework. Built off a different codebase it clocks in at about 7KB. It does one thing, and does it well.
Shadowbox serves a different, complimentary purpose, expanding greatly on the simple functionality LIghtbox is known for. It allows for modular display of images, image sets, flash, flash, video, quicktime and wmv (which worked great on my mac).