Captify is a jQuery extension for adding sexy captions to your images.
The plugin is very small (2.3 kb), and, although it mainly does one thing, it does it right.
Captify has some options available.
You can set the speed of mouseover and mouseout animations; change the opacity of the overlay; specify the classname to avoid CSS problems; and even change the location of the overlay.
P.S. We know that Webification is laced with jQuery this week–but so is the web! ;)