Ebates
Founded: 1998
Sign-up bonus when using our link: $10 (https://goo.gl/esXfBx)
Mobile app: Yes
The great-granddaddy of cash-back services, Ebates is the best of them all. It offers some key benefits: shopping via mobile app in-store rebates in addition to online ones writing. It automaticly gives you up to 70% cashback on eBay, Amazon and 6000 other online stores.
But if you enjoy the occasional trip to the mall, you can score cash-back savings by linking a credit card to your Ebates account, then activating in-store offers before you shop.
I also like Ebates' browser plug-in, which immediately alerts you when cash-back savings are available and even gives you an at-a-glance account overview. It saves you having to detour to the Ebates sites when activating purchase-tracking. It sometimes finds coupon codes for you as well.
You'll have to be patient, though: Ebates pays out quarterly, and your two payment options are mailed check and PayPal. This is the service I typically recommend for anyone new to cash back.