For a while I worked for a small niche service phone company which required me to work every other weekend. I always saw that as a huge perk. When I wasn't busy I surfed the net for coupons, entered sweepstakes, learned all sorts of interesting things on the net, researched plants ...
Did I mention they provided the best Columbian Coffee and a well stocked kitchen - the owner was Columbian and loved his coffee as much as I do.
About two months after I left the company - I received notice that I had won a huge Sony TV, surround sound, DVD, the works, it took me a second to realize this was the result from entering all those sweepstakes on the weekends.
Online surveys and blogging or writing that e-book are all possibilities.