I usually hate pop-up windows but I am captivated by this Highslide JS - JavaScript thumbnail viewer. From the site:

Highslide JS is an open source JavaScript software, offering a Web 2.0 approach to popup windows. It streamlines the use of thumbnail images and HTML popups on web pages. The library offers these features and advantages:

• No plugins like Flash or Java required.
• Popup blockers are no problem. The content expands within the active browser window.
• Single click. After opening the image or HTML popup, the user can scroll further down or leave the page without closing it.
• Compatibility and safe fallback. If the user has disabled JavaScript or the JavaScript fails in any way, the browser redirects directly to the image itself or to a fallback HTML page. This fallback is able to cope with most exceptions and incompatibilities.

It sounds too good to be true but the proof is in the pudding: it’s very refined and smooth. Unfortunately it will probably be abused by some site designers. Nonetheless, I need to go find a place to use it.