MileBlaster ($5.99)

No doubt that Frequent fliers carefully track their airline miles. With MileBlaster, you can obsessively keep tabs on your total number of earned miles and calculate how many miles you need for elite status. You can also receive alerts when your miles are due to expire and calculate how many miles you'll earn for a trip. MileBlaster is expensive, but it works with a wide range of airlines.

MileBlaster also offers a Web site where you can track the same information. There's a $6.99 per-year fee to use the site, but you can use the app independently.