Originally Posted by JD Gumby
Not all that many, really. Some you pay for via advertising (for example, the "free" versions of the Angry Birds games), many others you pay for by giving up your personal information, allowing your location to be tracked, etc., etc... There are very, very few that are truly free, that you aren't paying for in some manner other (usually more exploitive) than cash.
There are other ways of generating revenue from media. A lot of people will simply pay for convenience or quality. People still buy public domain books and movies.
There are many models based on no direct payment such as ad-supported TV or micro-transaction supported games. Many very large MMO games are now free to play but you can buy special items and perks. These games are doing well in general and we will see more of them.