TIOBE Index (link)
Monthly index and statistics dating back to 1989. Results from the top 25 search engines (according to Alexa.com) are used to calculate the language popularity (see TIOBE definition).
This site offers two rankings: one search engine-based (How many resources exist in that language?) and one community-based (How many people talk about a language?).
The search engine-based results are composed from GitHub, Googe File Search, Ohloh, Craigslist, and Google Search.
The community-based results stem from Reddit, Slashdot, and Lambda The Ultimate.
PYPL PopularitY of Programming Languages (link)
Programming language top 10 based on Google Trends.
Nice graphical comparison based on questions posted on Stackoverflow and pushes on GitHub.