The big selling point of the Discover credit card is cash back, which is accrued on every purchase but spikes to a whopping 5% on purchases in rotating categories such as restaurants, movies, gas stations, home improvement, and holiday shopping. You have to enroll every quarter to receive the maximum bonus in that category (visit Discover.com for details). However, more than 200 online retailers participate in ShopDiscover, which activates the signature 5% Cashback Bonus on most purchases year-round. The bonus climbs as high as 20% in some stores. Use your bonus to pay your bill, make online purchases or convert the points into one of 150 brand-name gift cards.