I have heard (and researched to death) that American Express waives annual fees for active duty military folks. If American Express has a card that is right for you, then this would be a great way to get the benefits without having to pay their often hefty annual fees.
American Express has changed its overall strategy over the last few years, and it now offers a wide range of cards that fit almost every need. Keep in mind that historically, American Express cards have been charge cards, not credit cards. A charge card requires the balance to be paid in full each month. A credit card has a provision for the balance to be rolled over to the next month. While American Express now offers both charge and credit cards, you must be absolutely sure that the card you choose is the right card for you.
Another issue with American Express is interest rates. If you choose a charge card, their interest rates are not great. In fast, some serious card shoppers might say that they are terrible. So, if you do ever carry a balance, these are not the cards on which to do it.
As I write this, I can see that this "no fee for military" is really only a good value for a certain type of customer: one who pays their bill in full each month and can get good benefits from a particular card. This might include certain rewards programs or other benefits.
As of this writing, I have not been able to verify whether this offer is available to National Guard or reservists. If you have experience with this, please tell us in the comments.
Thanks to Sarah, for pointing out that I failed to tell you HOW to get this benefit. As far as I know, you just call customer service and request it. I've even heard that you can get it refunded for prior years. How cool is that?