If you have an android phone, go and download Google Opinion Rewards. This application will give you surveys to answer every few days for you to answer.
In just under 2 years, I have earned $45.69 from this application. This has allowed me to buy books, some applications and some add-ons for applications as well. Now $45 may not seem like a lot but that is free money, that I earned by answering simple survey questions.
The survey money lasts only one year but if you use your phone a lot you will find ways to spend this free Google play money before you lose your cash.