Powerful search engine, especially if you know the following.

• site:stonybrook.edu   searches only a certain site
• site:.gov   searches only a certain domain
• -bush   omits results containing certain word
• +1   forces a search to include a potentially common word
• 28 fermimeters in parsecs   Converts any units
• ~expand   searches for plural and alternate tenses of given word
• ferrets | hedgehogs   returns pages containing either ferrets or hedgehogs or both
• filetype:pdf   returns only pages in pdf format (also use doc, tex, txt, ppt, etc.)
• "optical vortices are fun"   searches for pages containing all the words in quotes in that order
• allintitle:Hecht's Optics   searches for a page with the specified title instead of anywhere (automatically assumes it's a phrase)
• allintext:Brian Greene   searches only the text of a page (automatically assumes it's a phrase)
• allinurl:penguin   searches for a site with the specified word(s) in the site's address (assumes it's a phrase)
• -(pork beef sausage) tofu   use parenthesis to seperate aspects of your search string
• link:mozart.org   finds sites that link to the specified site
• 600..700 nm   .. searches a range of numbers, in this case from 600 to 700 nanometers
• movie: skesis   searches movies for quotes, characters, content, etc.
• Local - search for something in a specific zip code
• Froogle - search for stuff available for sale
  
  See Google's own shortcuts page.