My quick searches:

• The obligatory Google (g)

• Google this domain (gd): use google to search the site you’re currently at.
• Merriam-Webster (d)
• Wikipedia (wp)
• IMDb (db)
• Amazon (az)
• Netflix (fx)
• tinyURL (t): type the keyword in front of a long URL to get a tinyURL.
• Flickr (fl): Search for photos on flickr.
• Reverse Directory (rd): look up phone numbers—cheap caller ID.
• Urban Dictionary (ud): look up slang.

I love these things, obviously. Why have a honking big search bar or search sidebar when the browser comes with a space for user input already, namely the address bar? I didn’t even know this until researching this post, but in Firefox you can actually just right click on any GET form to create a quicksearch. Genius.