Danny the Deal Guru says that promo code EP1UBERCAR20 is good for $10 off your next Uber ride taken by December 1.
In the Uber app go to Payment and scroll down to ‘Add Promo/Gift Code’. I had no problem adding it to my account. This certainly won’t last.
Googling the promo code I see a suggestion that it’s actually for Uber Express Pool in San Francisco or Boston, so your mileage may vary.