Chase Manhattan Bank offers a Mastercard credit card tied in to Continental's OnePass. They also offer a debit Mastercard. Unlike the credit card, which offers one mile per dollar spent, the debit card offers a mile for every $2 spent.
If I remember correctly, Midwest Express also offers an affinity MasterCard.
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AlphaSigOU
Causa latet vis est notissima - the cause is hidden, the results are well-known.