The Citi Diamond Preferred Rewards AMEX has a special signup offer:

• Earn 2 ThankYou Points for every $1 spent on purchases for 12 months. After that, earn 1 ThankYou Point for every $1 spent.
• Receive bonus ThankYou Points when you spend more
• Spend $400-600 within 6 months of account opening and get 3500 bonus points redeemable for a $25 gift card
• Spend $600-800 and get 6000 bonus points redeemable for a $50 gift card
• Spend $800 or more and get 10,000 bonus points redeemable for a $100 gift card
• 0% APR on balance transfers until July 1, 2008.

Sign up at signup.citicards.com and use offer code F1F4, or call 1-800-655-4708 by August 15, 2007. (Via SD.)

Please note that this offer has expired. For the current offer, please see this link.