I have two different AMEX cards and looked up special offers. Nothing is appealing to me (consumer sucka spending), but how often do these offers change? Some might be worthwhile.
I think what you're really asking about are the "Amex Offers" that you can add to your card to get credits for shopping at certain retailers, right? New ones come out all the time, but some are limited so you might not get it at all, or only on one card. Right now, none of the offers are appealing to me, either, but there have been some awesome ones so far this year:
$15 back for $15 spent at Amazon - I bought a GC, then applied it to my next order.
$5 back for $5 spent at Google Play - used to reduce the price of a music purchase I was going to make anyway.
$20 back for $20 spent at Sam's Club online - got a bunch of home products for free ("paid" extra 10% for not being a member ... but it was all still free in the end).
$10 back for any spend at NewEgg - gift cards and some cheap things I had on my Amazon wishlist I managed to get completely free.