With flight costs going up by the week it seems, many people are flying with their miles.

Whether it be with miles-specific credit cards, offered by Capital One, TD Bank or other merchants, or airline-specific programs, racking up those miles is the key to a free ride.

However, what most people don't know is that using an airline-affiliated merchant, either in store or online could mean, not just one mile, but four, or even more miles.

For those who think that these merchants aren't real stores that people would buy from, that would be a wrong assumption.

These shops include big-name companies, like Apple, Nordstrom and Macy's. On the online side of things, there are overstock.com and Amazon, just to name a few.

To take advantage of these savings, just go to the airline's frequent-flyer website and scan their promotions and deals.

The miles could be a staggering amount during the Christmas shopping season when some airlines offer anywhere between 1,000 to 2,000 for purchase at different retail or online stores.

Last shopping season, United/Continental was offering 1,500 extra bonus miles for any purchase of $125 at one of their affiliates' stores and 500 more miles if you also downloaded the site's Shopping Assistant tool. And some merchants even let the consumer earn miles by shopping in store or by phone rather than online. You just had to register your credit cards with the store via United's site, stated Frommers.com.

There isn't a weird catch to make it too good to be true either. If you want a new iMac and go online to shop for one the price you pay for a new iMac via Apple's website is exactly the same as the price via the airlines' sites, according to Frommers.com.

It isn't just a few merchants, there are hundreds that participate in these mile offers. Below are some of the offers either active or were active last year.

Delta Airlines

United (Continental) Airlines

  • 3 miles/$1 at Nordstrom
  • 3 miles/$1 at Sephora
  • 3 miles/$1 at Bluefly.com
  • 2 miles/$1 at Avon
  • 1 mile/$1 at Apple

American Airlines

  • 11 miles/$1 at Teleflora
  • 6 miles/$1 at The Body Shop
  • 5 miles/$1 at Nordstrom
  • 4 miles/$1 at Old Navy
  • 4 miles/$1 at Drugstore.com
  • 2 miles/$1 at Wal-mart

US Airways

  • 4 miles/$1 at Drugstore.com
  • 4 miles/$1 at Jos. A. Bank
  • 2 miles/$1 at Old Navy

JetBlue

  • 2 points/$1 at Nordstrom
  • 1 point/$3 at Apple
  • 1 point/$1 at Godiva
  • 200 points/new or renewed pre-paid service at Verizon Wireless

The list is courtesy of Frommers.com.