For developers, Google releases a Code Search like Krugle or Koders. It was expected from a long time as google has the biggest database of code directories. For now, it looks like it is following things what Krugle or Koders have been doing. The source codes it searches in are definitely the huge open source collections available on the internet like SourceForge, Freshmeat and many others.
To search, you need to use Regular Expressions which are better described here.