Free Google play credit in return for your opinions (and marketing data for Google).
Answer quick surveys and earn Google Play credits with Google Opinion Rewards, an app created by Google Consumer Surveys.
Getting started is easy. Download the app and answer basic questions about yourself. We'll then send you surveys around once a week, although it may be more or less frequent. You'll get a notification on your phone when a short and relevant survey is ready for you, and can receive up to $1.00 USD (or local equivalent) in Play credits for completing it. Questions can range from, "Which logo is best?" and "Which promotion is most compelling?" to "When do you plan on traveling next?"
This is currently available to users located in the United States, Canada, United Kingdom, and Australia.
I wonder if Google+ is required. As of last year Google don't seem to value my opinion unless I have a Google+ account, which I refuse to open. Seeing as it's impossible for me to rate or review software on Google Play, I simply don't do it anymore.