Search Keys lets you go to search results by pressing the number of the search result instead of clicking. You can press 1 to go to the first result, Shift+2 to open the second result in a new window, etc. It works with Google, Google News, Google Groups, Google Desktop Search, and del.icio.us.
Update Oct 16, 2004: The shortcut for opening in a new tab is now Alt+N on Windows and Mac, to avoid conflicting with the Ctrl+N shortcut for switching tabs. It is still Ctrl+N on Linux, which uses Alt+N for switching tabs.