There are a lot of great credit cards out there (something I plan to write more about soon), in terms of the benefits you receive as a cardholder. But one of the consistently best source of great deals out there are "Amex Offers." Read on for more details, including a current free $20 offer ...
AMEX OFFERS PRIMER: As is often the case, I'm not going to re-invent the wheel here. Lots of other bloggers have written about American Express (Amex) Offers. HERE is the best "primer" I've found for beginners. It's a bit long to read, but VERY much worth it.
BEST CURRENT AMEX OFFER: At any given point in time, Amex has a lot (10-30) different Offers running that can be loaded onto your account (you can load as many of them as you want onto your card account!). As the post (above) describes, you must PROACTIVELY load these deals onto your account. It is really easy to do and "free money."
The best current example is described HERE and HERE. As Shawn points out, you never know how many of these Offers are going to be available, so it's best to jump on them (load them onto your account) ASAP. Once they are loaded, you have a set amount of time (through 9/30 in this case) to get the benefit. This particular deal gives you a $20 statement credit (free money!) after you spend $20+ at Samsclub.com (NOT in a Sam's Club Store - and note that there are some exclusions, like the photo department at Samsclub.com). Note that you do not need a membership at Sam's Club to shop on their website, but you will need to do a free one-day trial of their website and pay a 10% premium (or you can pay for a membership to not pay the 10% - and also unlock some features like being able to order eGift cards, including a current really good deal on Fandango $50 eGift cards).
After you spend $20+ at Samsclub.com, you will get a $20 credit to your Amex account, usually within a few days.
GOING FORWARD: This Samsclub.com deal is just one of MANY that Amex has on an ongoing basis. Usually they aren't quite so generous, often more along the lines of $10 off $50 at online or bricks & mortar retailer. But if you're going to be shopping at that retailer and spending $50, why not get $10 off?!? And every so often, Amex runs a great deal like the Samsclub.com one. (I have personally saved/made hundreds of dollars over the past year taking advantage of Amex Offers!)
The best Amex deal each year is Small Business Saturday, which is on the Saturday after Thanksgiving each year. HERE is a writeup about last year's SBS Offer.
KEY HINT: Get as many Amex cards as you (reasonably) can! Since each and every physical card you have can be registered for each deal. This includes secondary (authorized) users on an account, such as a card that your spouse has on your account. Another great card you can sign up for (for free!) is an Amex Prepaid card, of the "BlueBird" or "Serve" variety (unfortunately the Amex Prepaid Red Card from Target does not have access to Amex Offers, at least not yet). And those cards can also have free authorized users (including children aged 12+).