Google does offer CodeSearch, but, according to Krugle CEO Larsen, his company's technology looks inside to find the contents of code and can understand the different between a function call and a call definition, and even a code comment. Thus, its results provide pretty meaningful rankings.
Krugle's public search engine is the largest index of open source code anywhere, scanning more than 2 billion lines of code. But an enterprise version searches within an enterprise and matches the results with external open source code. The public version is free, and the company charges for the enterprise side.
The company has also managed a great array of partnerships that show the power of this technology. First, it works with entities like the IBM developer network, Yahoo's developer network and Amazon, among others, essentially powering their code search (it also powers SourceForge.net's code search). And then it works with IBM's Rational and with CollabNet to ensure that it's optimized for crawling these source code management systems.
Larsen says that enterprises use Krugle for things like bug fixes, impact analysis, and discovering history about code when developers leave the organization. One large company with more than 1 TB of code saves itself almost $10 million a year just in tracking down bugs.
(Uh, maybe it had better get some better developers.)