If you link your PayPal account to your Uber account, you will get $15 off your next Uber ride when you pay with your PayPal account (excludes UberTaxi) through 11/28/13. For more information and restrictions, please head here.
Note: I linked my PayPal and Uber account the other day, and I had to commit to always pay with my PayPal account. I’m not sure if this can be changed in the future, but something to keep in mind if you don’t want to pay with PayPal or need to switch between credit cards.