If you order large amounts of coinage via credit card, the US Mint sends it to you free of charge, which means that you can turn around and deposit the money in the bank, and, if you have a credit card with reward miles, you still get those miles, for buying money, which you use to pay off the bill:

Enthusiasts of frequent-flier mileage have all kinds of crazy strategies for racking up credits, but few have been as quick and easy as turning coins into miles.

At least several hundred mile-junkies discovered that a free shipping offer on presidential and Native American $1 coins, sold at face value by the U.S. Mint, amounted to printing free frequent-flier miles. Mileage lovers ordered more than $1 million in coins until the Mint started identifying them and cutting them off.

Coin buyers charged the purchases, sold in boxes of 250 coins, to a credit card that offers frequent-flier mile awards, then took the shipments straight to the bank. They then used the coins they deposited to pay their credit-card bills. Their only cost: the car trip to make the deposit.

Neat scam, and as always, the only problem is that I discover it too damn late.