Valve's Steam service took in almost $1 billion USD, according to Forecasting and Analyzing Digital Entertainment , where they say: "Estimated revenues through the major digital PC retailer were estimated at $970 million USD in 2010, with December capping off the year with an estimated $213 million USD." They offer a list of the top titles on the service, which was dominated by shooters:

Top Selling Titles, by Estimated Gross Revenues in 2010