Chrome: If you're used to being able to hit the forward slash key to access the search box in Google webapps, then you might be annoyed when it doesn't work elsewhere. SlashSearch is an extension that adds the keyboard shortcut to any site and if there is no search box it makes one.
It's a subtle extension but it makes custom searches on websites considerably easier. By default, hitting the forward slash key will take you to the search box on a site. When a website doesn't have its own search box, SlashSearch creates one and does a site-specific Google search automatically.