This one time I had to provide guidance on which web browsers to support on a future website. That means I need graphs and things!
Worldwide statistics pulled from 40,000 sites according to the FAQ. It provides some free data, and paid subscriptions which provide access to filtering. I liked this graph.
W3 Counter provides a free visitor tracking for websites, and posts their aggregated statistics on browser usage from their users sites. The data is not filterable or sortable, but it is easy read.
StatCounter Global Stats
Stat Counter is another visitor tracking service, and they also post their aggregated browser statistics. They include some sorting and filtering options for free.