Discover also has a "GetMore" program that gives you 5% cashback (which can be doubled to get GCs with certain companies) if you purchase things from certain categories. The categories change every quarter but are usually quite good. There is a cap I forgot what it is but it is fairly high (I believe $100 per quarter). Also, discover will be accepted virtually everywhere in 1-2 years because of a new contract agreement (that is when a merchant signs up for credit card acceptance it will be included with MC and VI).

Example from oct-dec:

Restaurants—From fast food to fine dining

Movies—From movie tickets to movie rentals

Books, Music and Everything Else
In-store or online from these specific retailers:
AMAZON.COM
Barnes & Noble
Borders®
Circuit City
Crutchfield®
Napster®
Waldenbooks®