Google offers free Spotlight importers for indexing source files for AppleScript, Interface Builder and Xcode projects. If you work (or play!) with AppleScript, Interface Builder or Xcode – then check out the Google Toolbox For Mac Spotlight Importers.
Mac OS X provides native support for the popular ZIP archive format. But have you ever wished Spotlight would search the file names inside your zipped archives? That’s precisely what the free Ziplight Spotlight importer plugin does. Take a look.