TinyBox2 modal box script brings a ton of new features and still clocks in under 5KB. The script now supports iframes and images natively. You can POST with Ajax. Clicking ESC will close the window. Callback functions can be passed for load and close events.
You can set CSS IDs to override the default styling. CSS position can be toggled between fixed and absolute. The mask opacity can be sent. You have full control over window location. And of course there is now a close button out of the box you can toggle.
This script is tested in IE7+, FF, Chrome, Opera, and Safari and is available free of charge for both personal or commercial projects under the creative commons license.
License: Creative Commons License