Amex is also well know among the points and miles community for running their "Sync" program. That allows you to link your Amex card to your Twitter or Facebook account and sign up for rebates offered by Amex.
For instance, Amex has a Twitter Sync deal with Sony right now that gives $25 off a $100 purchase, including gift cards. Each of your Amex cards (including authorized users) is eligible, if it is synced to a separate Twitter account. Here's the way I've played it.
1. Sync card to Twitter @ sync.americanexpress.com.
2. Tweet "
3. Click-thru Ebates.com to earn 6% back on Sony purchases (including physical gift cards but not e-gift cards)
4. Purchase $100 Sony gift card, pay with Synced Amex ($25 will post 1-2 days after transaction posts)
5. Once GC arrives, sell to Plasticjungle.com for $78 after click-thru from Topcashback (earning 2.5% on the sale)
Total Take $110.95 for a profit of $10.95 per card. You can do this once per card, provided each card is synced to a separate Twitter account. Plus you earn the points for spending $100 on each of your Amex cards!
Of course, as Heinlein observed "There Ain't No Such Thing As A Free Lunch." TANSTAAFL stands for the principle that nothing is ever truly free. If you carry a balance on your credit cards, deals like this probably don't pay off. Also, even if you don't end up losing any money on the deal, there is always the opportunity cost of spending your time chasing the deal. For me it's a hobby and sneaking up on the deal is its own reward.
Update: I see that Sony.com is not offering a free $20 e-gift card for each $100 e-gift card purchased. That would eliminate the $6 dollars that you can earn through Ebates, but, if you actually want to purchase something from Sony, it could make the deal more lucrative.