Just saw this today while filling up at a Chevron. Discover cardholders can get 5% cashback at Chevron and Texaco gas stations from now until March 31st, 2014. Subject to a cap of $250 in purchases. Must sign up first by going to Discover.com/chevron and then logging into your online account. The next screen should look like this:
This is in addition to the standard 5% back categories on the Discover it card, currently 5% back on up to $1,500 in purchases at restaurants and movies for 1st quarter of 2014. The Chase Freedom card also has gas stations as one of their 5% back categories for Q1 2014 if you have that card (good for up to $1,500 in purchases).