Recommendations for credit cards in the USA with cashback rewards?

I've had the same secured credit card through my bank for years; I only use it for car rentals and when my debit card gets declined on international online purchases. It's very easy to maintain as there are no fees and I always pay off the balance within the week; however, there are also no rewards. I know that a lot of credit cards out there have cashback rewards, and it seems like kind of a waste not to take advantage of that. But there are so many different ones that it's horribly overwhelming for me to try to research which one(s) might be a good choice. Costco has one which would have probably been an easy choice if I were able to spend more money there, but as of currently I have very little space and only hold a membership for gas.

So, do any of you lovely folks have recommendations to give me a starting point for what to look into? What cards have you used and been happy with?

ETA: I am in the US!