A fun game if you like music.
An app that plays some characteristic part of a song or music piece (the beginning few seconds, the bass line, etc.), and you have to identify it as quickly as possible. You can invite friends to a challenge. Leaderboards show the best overall, by music genre, decade, etc.
More sales and more profit.
Have only very low and very high price versions of the product or service. For instance, a book even by a known author as an ebook would cost under $5 (preferably $1), while the deluxe hardbound printed edition would be $30-$90 or more.