American Express offers 20,000 when you sign up for a Gold Delta Skymiles Card with your first purchase. Better yet, sign up for 2 more cards and get another 5,000 miles. That's up to 25,000 bonus miles and one of the best offers we've ever seen from them. It's worth getting the card for the free checked bag on Delta flights alone. You'll also get one bonus mile for every dollar spent on select purchases, double miles on Delta purchases, and more. Plus, there's no annual fee for the first year (a $95 annual fee applies for each additional year, but saving the cost of checked baggage fees more than makes up for it).