Apple has created a new section on the iTunes Store called "Free on iTunes" which lists music and full length TV show episodes that users can download for free. The section currently includes 16 singles from the likes of Machine Head, Rogue Wave, Asking Alexandria, Nude Beach and more, as well as select full-length episodes from shows such as 12 Monkeys, Backstrom, The Musketeers and more.
After removing the "Single of the Week" promotion at the start of the year, the "Free on iTunes" section is likely the best way to access free content from the iTunes Store going forward. Head to the link below to see all the content that's currently available.
Source: iTunes Store (Free on iTunes)