jQuery validation plug-in - main demo. jQuery lightbox for images, videos, YouTube, iframes. Jquery-swapimage - Project Hosting on Google Code.
Part of slick applications is images. They might be part of the content being loaded or something like an icon in an application. But, for those images being added after the page is loaded there can be a time gap while that image is downloaded. To avoid those time delays the images can be preloaded in the background.
Lets take a look at how to do that. Use jQuery - Showcase of sites that use jQuery.