I'm not a big fan of search bars but I'm addicted to Quick Searches. This feature allows you to define a keyword (or 1 character) to search a site. For example I've set the letter 'g' to mean Google search, so when I type g search_string in the address bar (shortcut CTRL+L) I search Google.

To setup quick searches go to the quick searches folder under bookmarks, right click on a bookmark, select properties and type in the keyword in the keyword field. The other two I really use are the d for dictionary.com and w for wikipedia.