I have a "goto" rewards card through Pentagon Federal Credit Union "Platinum Rewards Card" that give points -
5 points for GAS per dollar spent -- ( I average 1500 points per month in gas points )
3 points for Supermarket per dollar spent ( I average 1000 points per month in grocery points )
1 point per dollar for all other purchase ( I average 2000 points per month in other category points )
-- I then spend the points to buy visa gift cards 10,000 points is $100 card
HOWEVER If a credit card company sends me an "offer" to open a account and spend, say, $500 within first three months for $100 cash then I grab it, do the deal and then close the account after rewards are cleared

I have gotten well over $1000 in cash rewards this year doing this

I have developed a little system of keeping track of the offers and timing so I maximize my return on any time spent doing the deals

closing the accounts is the key because then it just resets you in their computer and a couple months later BAM another offer

I have also opened a chase checking account for a $200 dollar bonus deposit ( only hitch was keep it open 6 months and deposit $1500 to keep no fees) no direct deposit was required -- easiest way to get my cash $$ working for me!

Also I watch my credit score and it has NOT been hurt at all and I have been doing this system well over a year.

I have also done a CC deal and gotten $400 off airfare this year