Early on, when Google had to convince us that the Play Store was worth our time, we got apps and games for 10 cents. There were sales where content was just 25 cents, or full albums for just $2. But recently, the sales have offered more in terms of in-app benefits (which are useless if you don't use the app), free single music tracks, and maybe a free book (that may or may not technically be on sale).
This time around, there are some okay in-app offers (if you use the apps). Fancy will give you $15 towards a purchase, Hotel.com gets you 10% off, Gyft will double its usual offer and give you a $20 gift card, then there are specials for Royal Revolt, Gnome Village, and Yumby Smash. As far as music, you can get Sweet Jane by The Velvet Underground, or All My Friends by LCD Soundsystem for free. Kung Fu Panda is half off, the pilot of Breaking Bad is free, and the one book available is A Quest of Heroes by Morgan Rice, which is free.
source: Google Play