I seem to keep about $1600 in gift cards on amazon at any one time.

I have Citi Forward for 5%. I got this two months ago by converting my old Citi Platinum card. I just told them I was planning on going back to college full time and thought the card would be useful.

Chase Amazon is the obvious runner up at 3%.

4th Quarter - Chase Freedom Amazon 5% on first $1500. Discover Online Shopping 5% on first $1500.00.

I accumulate a gift card balance because I take advantage of short-term deals. In the past few months, Quiktrip has offered $5 off $25 Amazon GC (20% discount + 2% gas CC rewards). Best Buy has/had a deal with the Amex/Twitter thing where you got a $25 statement credit for $250 in purchases. You can buy kindle GCs at Amazon. Some grocery stores will periodically run deals like "buy $100 any gift card, get $20 coupon for groceries on your next trip."

I actually haven't used my forward yet because I'm still using up all of the 10%+ amazon money.

And, yes - Subscribe & Save is the best when you add Amazon Mom. 20% off every month for a delivery of 5+ items. I've never seen diapers, wipes, and formula so cheap. I also buy staple items for my household - pasta in bulk, pasta sauce, rice, ziploc, paper towels, toilet paper, garbage bags, detergent, pods, and kind bars!