From Expedia's web site

1,000 Great reasons to book your trip with Expedia.com™ and the American Express® Card!

Earn 1,000 American Express Membership Rewards® bonus points when you book your first trip with Expedia.com!
Expedia.com is a full-service online travel agency that's convenient, easy to use, and helps you feel confident you're finding the right trip at the right price. And if you're enrolled in the American Express Membership Rewards program, we can make it even more rewarding with bonus points! All you need is an eligible, enrolled American Express® Card and you're on your way!
The Right Trip At The Right Price, Plus Membership Rewards Points!
The first time you purchase an airline ticket online through Expedia.com, you'll earn 1,000 Membership Rewards bonus points from American Express. Use an eligible, enrolled American Express® Card between 15 September and 15 November 1999 to purchase your ticket. Your 1,000 Membership Rewards bonus points will be credited to your account within 12 weeks.

Want to learn more about the American Express Card Membership Rewards program? Go to: http://www.americanexpress.com/rewards.