Update 5/6/2014: Cashback is down to 2.45% on Big Crumbs and 2% on Top Cashback
Big Crumbs has increased the payout rate for American Express gift cards to 3.5%.
If you use your American Express Fidelity to pay and promo code FPMOM (promo code works until 5/15), you will get 5.3% cashback on a $5,000 purchase of gift cards.
If you want more info, you can see my other post where Top Cashback is offering 3% (today is the last day for that). In addition, you can get up to 6.4% back using the Barclays Arrival Card.