How do I add Wikipedia as a search provider for the Safari search bar? In Safari, when I click on the magnifying glass in the search bar I get a menu, the bottom of which lists Google, Yahoo!, and Bing. I'd like to see Wikipedia here too, and get results returned from the Wikipedia website.

FYI, I'm using Safari 5.1 on Snow Leopard.
There's a plugin for Safari called Glims that lets you add different search engines (including Wikipedia) to the search bar among other tweaks. You can read about and download it here.

Here's a post on someone's blog that details how to install it and set your search engines to what you want.

Hope that helps!