Ask HN: Good Programming Search Engines?

Does anyone have any recommendations regarding a good search engine specifically for programming topics? Ideally one which returns discussions or blog posts, rather than source code, explaining concepts, terms, and potentially discussions programmers have online. All non-programming results would be filtered out.

For example, Google "register" or "auto". These are C Storage Class Specifiers, but nothing relevant to C appears in the first 10 results. They're buried under lots of unrelated content. You can slap "+C" and "-C++" to get more specific, but you can quickly amass a very bloated query string. Copying/pasting programming terms out of a PDF for a quick search becomes cumbersome in some cases too. Google/Bing don't appear to have a filter to blot out all non-programming results.

There are plenty of source code search engines out there:

www.google.com/codesearch

www.koders.com

www.github.com

www.bitbucket.com

...and some community forums which do have great content:

www.stackoverflow.com

www.experts-exchange.com

...but no single centralized "Google for Programming". What search engine(s) do you recommend for programming topics? Do you have any search tips/hints to offer others?