Yesterday I found a great code search engine - Krugle.
Krugle has great AJAX interface, tabs that allow you to open more search results in the same page, syntax highlighting and an easy way to browse within a project directory. Krugle also has a search engine for tech articles and documentations.
Another great utility from Krugle is that you can search on specific code features such as function calls, function definitions, class definitions and comments.
However, Krugle's disadvantage (when compare it with Google Code Search) is that Krugle has a less comprehensive index and doesn't support regular expressions for queries.