This was posted at another site:
U.S. Mint Online Product Catalog
The US Mint sells $250 boxes of $1 coins for face value with free shipping. You can buy them with a rewards credit card and get the points for the purchase. Then, when you get the coins, just deposit them back into your account. The result will be $250 worth of reward points for zero cost.
The only downside is they limit you to $500 worth of coins.
Can anyone see any flaw in this plan?