Get 25000 bonus miles with the Escape Card by Discover that can be exchanged for $250 credit on your travel. However, you can only get 1000 miles for each month you make a purchase. Most convenient way would be put a recurring charge with your cell phone using this card. According to their Rewards program, you get two miles for every dollar spent on all purchases.
Once you have accrued 25K miles, simply book any flight, cruise, hotel, etc so that miles can be redeemed. You log into your account, select the total miles to redeem for credit toward your credit card. The miles could also be redeemed for cash or gift cards, but you could lose up to 50% of the potential value. You can also use this card as a primary car rental insurance.
The downside of this card is the $60 annual fee. If you actually go through with this card for two years, the total bonus is actually $120 total credit after the annual fee. Instead, you might want to check out the Discover Miles with no annual fee for 12000 bonus miles.