Affinity credit cards -- that is, a card tied to a certain organization -- are a big moneymaker for the airlines, and even if you don't really need another credit card, you'll see some enticing sign-up offers designed to lure new customers.

When choosing a card, look at the bonuses being offered, consider how often you fly on the airline and consider the other businesses or carriers with which the airline is affiliated.

Note that many cards waive the annual fee for the first year, and spending with an affinity card is an easy way to keep your miles active. But some airlines do charge additional fees when you try to redeem your points so that free ticket will cost you more than you might plan. Here's a look at some of the cards. To look at others, go to websites such as Creditcards.com, Cardratings.com or Bankrate.com, or Google "credit card comparison."

Southwest is offering 50,000 bonus points if you sign up for a new Rapid Rewards Plus Visa by Thursday. That number of points would convert to US$800 in Southwest's Wanna Get Away fares. The annual fee is US$69, and it is not waived for the first year.

I like the flexibility of the Rapid Rewards program. The points are not restricted on holidays or peak summer dates, though you will likely be using more points during those times, but not nearly as many as double the miles you often see required on the legacy carriers during peak times.

The American Aadvantage is offering a bonus of up to 40,000 miles, plus a US$100 statement credit for new cardholders with certain spending requirements. Typically the annual fee of US$85 is waived for the first year.

British Airways is offering a US$100 credit if you dine twice at a one-, two- or three-star Michelin-rated restaurant in New York City through the end of the year. Participants include Jean-Georges, Gordon Ramsay at the London and L'Atelier de Jo?l Robuchon. Taxes and fees on British flights can be steep, so you may not want to use them on international flights. But you can use the miles for domestic flights and to Canada, Mexico and the Caribbean on partner airlines American and Alaska.

The American Express Membership Rewards program is flexible. You can use your points to buy travel -- for example, a US$100 fare will cost you 10,000 points, or a US$300 fare will cost you 30,000 points -- or you can transfer points to your choice of participating airline or hotel programs. The annual fee for the green card is US$95, and the first year is waived.

The annual fee on the Platinum Card is US$450 a year, but the perks more than make up for the cost. You get 20% of your points back when you use points to pay for your travel; you get free entrance to American, Delta and US Airways airport clubs, and you qualify for up to US$200 in credits annually for airline fees such as baggage, reservation change, in-flight food and beverage and phone-reservation fees and more.

If you travel internationally, you can also be refunded the US$100 fee for the Global Entry expedited entry, a U.S. Customs and Border Protection program, when you pay with your card. The fee for the Platinum Card is not waived.

Before you sign up, contact the issuing bank or institution and ask what other promotions may be available, because you may find an even better bonus.