Windows Desktop Search

or

Google Desktop

You decide.

Check out these posts too:

  1. Windows Desktop Search 3.0 Beta Engine Preview
  2. Google Desktop 3 Beta Released
  3. Google Desktop 4
  4. Windows Desktop Search: Internet Explorer History Add-in
  5. Google Desktop 2 no longer in beta
  6. Windows Desktop Search 2.6.5 Released
  7. MS Windows Desktop Search add-ins