I have a Discover it card, and I earn a couple hundred bucks a year manufacturing spend on it in the card's rotating 5% cash back categories (quarters 3 and 4 were good for $75 each last year). Plus, having a card gives you access to the Shop Discover portal, which quite frequently has some of the highest cash back payouts, including at relatively "rare" merchants like the Apple Store. Since Chasing the Points killed the Upromise cash back portal, Shop Discover is now perhaps the best place to click through to Staples for all your gift card needs.
In case you're considering applying for a Discover it card, I want to point out that it appears there's a $150 signup bonus available if you apply through certain links. I've had the card forever, and actually signed up for the card when it was the Discover More, so I can't attest to whether those applications actually work for a $150 signup bonus. But at the bottom of the application you can see the text:
"TERMS OF CASHBACK BONUS OFFER: Get a $150 Cashback Bonus after you make $750 in purchases within the 1st three months from account opening. Promotional award will be applied within 8 weeks. The promotional award is in addition to the Cashback Bonus earned on all purchases. Only valid for new applicants that use this offer link."
I've updated the link on my cash back resource page as well.