Cardamom is also commonly used in the Middle East with coffee.
For example in Israel you often see kafee im hel on the menu of a coffee shop, hel being the Hebrew name for cardamom. In Arabic it is called hal or hail.
As a member of the same plant family as ginger (the Zingiberaceae family), cardamom is very aromatic and slightly sweet. In my opinion it smells a bit like orange. As the essential oils that give cardamom its flavour and smell evaporate quickly cardamom is normally sold as pods.
Cardamom is undervalued in the west, even though it's one of the oldest known spices. In the Middle East it is used a huge amount (60% of the world's production of cardamom is shipped to Arab countries) both in cooking and for making coffee.
There are several ways to make coffee with cardamom. Normally freshly ground seeds are added to the ground coffee or whole pods are put in the pot. Bedouins also have special coffee pots which hold the cardamom pods in their spouts so that coffee doesn't come into contact with them until the moment it's poured.
That was the factual part.
I personally find that the addition of cardamom to coffee makes the coffee very smooth and slightly dry, whilst masking any bitterness and also disguising the strength of the coffee.
My personal favourite is to take 1/2lb of Java (a very dark and strong roast) and add to it 1oz of cardamom and then mix the two evenly and store it. I've found from experience that making a large coffee with this in a stove top espresso machine creates a wonderfully strong and smooth coffee. This coffee has no bitterness and a slight flavour of orange. A large mug (my mug holds nearly a pint) of this makes you very alert and quite wired but in a very easy and smooth way. I was slightly concerned that I could still feel the effect about six hours later, and I'm quite a hardcore coffee drinker.
Drink it at your own risk, but it is one of the most wonderful drinks you'll ever have.