Most of us use our reward credit cards to earn points and miles towards trips by purchasing everyday items. Charging food, gas, groceries can add up quick.
In this Flyertalk thread some people have taken it to another level by purchasing US Mint dollar coins on their reward credit cards. The process goes like this. First wait until the beginning of your credit card cycle, purchase US Mint coins (with free shipping), receive the coins, deposit the coins into your bank account, then pay off your credit card statement.
This can be a great way to pad your airline or hotel account on a monthly basis. Be sure if you use this to use it responsibly by using the coins to payoff the credit card statement on a monthly basis.