There's an easier way to make money on credit cards. Well specifically, one credit card - the Bank of America Better Balance Rewards. Basically, you need to charge at least something every single month, wait for the statement to cut, then pay it off in full or make a minimum payment (well really, you should just pay in full anyway...). At the end of every quarter, if you have made at least a minimum payment or paid in full for each month in the quarter, then you get a $25 bonus. If you deposit the bonus into a BoA bank account, you get an extra $5.
So you can charge a couple bucks a month to this card, pay it off in full AFTER the statement cuts, and then earn $100 or $120 a year.
Best way to do this is open a BoA savings account if you don't already have one ($300 minimum to open), put a recurring fixed monthly charge on your credit card, and then schedule automatic payments. If you go this route I highly recommend that you open a BoA account, becuase if you don't, your rewards are issued as statement credits. WIth a statement credit, it'll throw off your automatic payments, and if you have a negative balance at the end of a month, it'll disqualify you from the rewards.
One perfect charge to put on this card is Netflix. These rewards would cover the cost of Netflix, plus some.