SafariKeywords teaches Safari a feature that’s long been available in other browsers, such as Mozilla or OmniWeb and is known as “Mozilla Keywords”. It basically lets you tell Safari where to search for the words you entered into the search bar, instead of always consulting good old Google. If the first word of what you entered is the name of a shortcut you defined (or one of the factory defaults) in the preference pane, Safari uses that shortcut’s URL instead of Google. If not, it defaults to Google.
For example, you want to look up your favourite actor at the Internet Movie Database, just go to the seach bar, enter “imdb de niro” and hit Return. Looking for vintage Beatles albums? Enter “ebay beatles album.” Shareware for your iPod? “macupdate ipod.”
SafariKeywords is freeware. More info and download link here.