Costco Amex is 3% for gas and restaurants, 2% for "travel" (hotels, travel fare), and 1% everywhere else. (Anomaly - It's 1% inside theme parks, even for food, but 2% if you pay for things in advance.)

Discover runs 5% promotions on various things that last a month or two. These things include gas, grocery, drug store purchases. However, make sure that you understand the terms. (Some of the travel promotions weren't much good because 5% only applied to the first $500.)