searchcode - A source code search engine
GrepCode - GrepCode.com is a code search engine built by developers for developers to search and browse open...
grep.app - grep.app searches code from over a half million public repositories on GitHub.
Open HUB - Open HUB is an open source directory that anyone can edit.
Sourcegraph - Sourcegraph is a free, self-hosted code search and intelligence server that helps developers find, review, understand, and debug code. Use it with any Git code host for teams from 1 to 10,000+.
Insight.io - Best web-based IDE-like source code browsing and search tool