Google Labs came out with CodeSearch : a search engine for public source code.

Since most of the time I work with Java I prefer Javaref which is more Java specific and gives the ability to narrow down the search to different packages and supports favorites etc. And it has a nice cool AJAX interface too.

There also Koders.com which provides language and license selection in the front page, unlike Google Codesearch which hides the options in Advanced Search.