The days of google codesearch are ended since a while, but now we have an up-to-date and open source debian codesearch.
(from the about page):
It searches all the open source projects which are included in the Debian archive (the "main" distribution only, not non-free or contrib). Currently, that includes about 18000 packages with 140 GiB of source code.
The search engine itself is based on Russ Cox’ codesearch tools, meaning it uses Regular Expressions as input. Like the codesearch tools, it was implemented in Go.
The project is a thesis so the source code won't be available until January 2013, and we all hope that the project continues beyond that date.