Citi now has an offer for 25,000 bonus AAdvantage® Miles when you sign up for a new AAdvantage® credit card and spend $750 within 4 months. The annual fee is also waived for the first year as part of this deal.
The offer can be found here and is valid until May 31, 2008, per FW.
Note that if you plan to spend at least $10,000 in a year on the card that there is another viable option available, with up to 40,000 bonus miles: 20,000 after spending $750 within four months, another 10,000 miles after spending at least $10,000 in the first year, and a final 10,000 bonus miles for spending at least $10,000 in your second year. That offer is available here and is available until November 30, 2007.
Alternatively, if you don’t want to spend $750 on the card, you can take advantage of this offer which will give you 15,000 bonus miles after your first purchase of any amount.