American Express' Membership Rewards program is often considered one of the best. That's because it earns miles you can transfer to several major airlines, among them Continental, Delta, and U.S. Airways. Combine that with smart use of airline partnerships, and that means your spending on Amex can get you free trips on Continental, Delta, Northwest, US Airways, and United. You also can combine your Amex charge cards, Optima credit cards, and Small Business charge and credit cards all into one Membership Rewards account. Plus, jetBlue recently joined Membership Rewards. That gives you a way to add points to your program with one of the best-ranked discount airlines.

One other suggested card: The Amtrak Guest Rewards Card. It's a MasterCard from MBNA. You don't have to travel Amtrak to use it, though you do get some Guest Rewards points for regular Amtrak train travel, and more for Acela Express/Metroliner trains. They partner with Continental, allowing transfers into Continental OnePass miles in blocks of 5000 miles, up to 25,000 miles per year. The card has no annual fee, unlike the actual Continental card. Remember, Continental is in the SkyTeam alliance, so those Continental miles are good for trips on Delta and Northwest too. One warning: Amtrak might drop the airline connection without notice – they already did it with United. Until January 2005, you could also transfer points to United Mileage Plus, but they dropped it without any warning.

A downside to both Amex Membership Rewards and the Amtrak MasterCard/Guest Rewards program, is you can't make use of the miles until you've earned enough for the minimum transfer level (1000 for Membership Rewards, 5000 for Amtrak.) Whereas on the actual airline cards, if you spend $100 next month you have 100 more miles. If you're only short a few hundred miles for a free ticket and need a "top-off", these cards won't help while the airline cards will. But with some planning, they can help you get a free trip quickly.