Airlines are deleting miles faster than ever. Flying keeps them alive--downloading an iTunes song does, too.

We've examined policies for eight domestic carriers and found many, many options for saving miles. In the chart at right (click to see the full chart), "Our Pick" is an especially easy way to keep reward points from disappearing--in some cases, you won't have to spend a dime. We're including each carrier's shopping partnership links because they're tougher to find than you'd imagine.

To purchase through some partner retailers, you must not only sign in with your frequent-flier number but also type in a special code before buying, as explained in the airline program's online mall. Pay close attention to detail to make sure that your account is credited. Within a few weeks, log in to your reward program account to check that the "activity" has been noted.

American Airlines

• Credit Card: Citi AAdvantage MasterCard, free first year, $50 annually thereafter; 15,000 bonus miles after you spend $250
• Shopping: aadvantageeshopping.com (240 partner retailers)
• Our Pick: Two bags of coffee via Starbuck's retail website, StarbucksStore.com. ($9.50)
  Correction: In the original article and the accompanying chart, we erroneously said that a participant in American Airlines' reward program could keep their account active by buying a gift card from partner Starbucks.

Continental

• Credit Card: Continental Airlines World Master-Card, $85 annually; 15,000 bonus miles with first purchase
• Shopping: continental.com/for/shoponepass (50 partner retailers)
• Our Pick: A year's subscription to music magazine Blender (400 miles)
• Our Pick: Digital photo from partner Shutterfly (19¢)

JetBlue

• Credit Card: American Express JetBlue Card, $40 annually; 25 TrueBlue points with first purchase
• Shopping: None
• Our Pick: Using the credit card extends the life of points for an additional year

Northwest

• Credit Card: WorldPerks Visa Platinum Card, $55 annually; 10,000 bonus miles with first purchase
• Shopping: nwa.com/mall (150 partner retailers)
• Our Pick: Take the five-minute quiz at nwa.com/worldperks/university

Southwest

• Credit Card: Southwest Rapid Rewards Visa, $59 annually; eight credits after first purchase
• Shopping: None
• Boo! Hiss!: Without exception, mileage credits expire after two years

United

• Credit Card: United Mileage Plus Visa, free first year, $60 annually thereafter; 21,000 bonus miles after you spend $250
• Shopping: mponlinemall.com (155 partner retailers)
• Our Pick: Groceries bought online through partner Safeway

US Airways

• Credit Card: US Airways World MasterCard, free first year, $79 annually thereafter; 15,000 bonus miles with first purchase
• Shopping: usairways.com/shop (75 partner retailers)
• Our Pick: Download a song or two at partner iTunes (99¢)

Read about our Travel Experts' Favorite Rewards Programs at BudgetTravel.com.

Note: This story was accurate when it was published. Please be sure to confirm all rates and details directly with the companies in question before planning your trip.