If you run a site that links to world of warcraft items, you're probably using the wowhead.com javascript to bring their item popups to your site. See it in action here, mouse over the "King Dred's Helm" link. It will popup Wowhead.com's info.
is this just a jsonp callback to their site?
I want to implement something like this on my site. Perhaps it could be done using jQuery html fragment and a jsonp callback to my own site?