Google turned off Code Search earlier this week. Creating and launching the initial public version of Code Search was my first project at Google, and, like many programmers, I'll miss it.
To mark the occasion, I have posted at swtch.com/~rsc/regexp/regexp4.html
an explanation of how Code Search worked, and at code.google.com/p/codesearch
a set of command-line tools to run regular expression searches against large amounts of code, quickly. It's obviously not a complete replacement, but it's the core of what Code Search did, and now you can run it on your own machine.
I want to thank everyone at Google who worked on or supported Code Search over the past five years. There are too many to name individually, but it was truly a team effort and a lot of fun.
P.S. Perhaps the best picture of source code ever published: blog.sfgate.com/techchron/2006/10/04/coders-start-your-search-engines/