Google Desktop

This is a free client application that provides full text search over email, files, music, photos, chats, web pages that you've viewed, and more. By making your computers searchable, Google Desktop puts your information easily within your reach and frees you from having to manually organize your files. Google Desktop for Windows also helps you gather new information from the web with gadgets and sidebar. (Google Gadgets are visually appealing mini-applications that can display anything from your new email to the local weather forecast to personalized news.)

http://desktop.google.com