I slapped this together recently using Chartbeat's realtime data (so the sources are major sites – nytimes.com, foxnews.com, espn, etc): http://percentoftheinternet.com
http://percentoftheinternet.com/windows http://percentoftheinternet.com/chrome http://percentoftheinternet.com/ie
...etc...
Raw data is here: https://api.chartbeat.com/cbtotal/?v=2