The Silver Searcher (or ag to its friends) has quickly become my go-to search tool for code. Performance gets top billing, but this tool has a number of other handy features. For example, searching ignores patterns in your .gitignore by default and ag is aware of a large number of programming languages and technologies. For example ag "search string" . --html searches only in files with the extensions .htm, .html, .shtml or .xhtml.