There are several different options: rockwool/stonewool, cocofiber, perlite, expanded clay pellets.

The style of system you are using will determine which media you will use. I will explain what each one is and what it is typically used for.

Coco Fiber ~ sometimes referred to as coconut fiber, and that's because that is just what it is. It is the shavings of coconut husk. It is a light airy media which is good for getting oxygen to the roots. It can be used by itslef or as an amendment. It is suitable for containers set on a drip system and for bubbling systems or ebb & flow systems using net pots.

Rockwool/Stonewool ~ this media is made from molten basalt and limestone. It comes in many sizes, from 1" to 6" cubes. It can also be purchased in sheets great for propagation. Rockwool is suitable for aeroponics, a drip system, deep water culture, NFT, and ebb & flow.

Hydroton Rocks/Grow Rocks/Expanded Clay Pellets ~ is referred by all three depending on where you are and who you are talking too. This works great as a stand alone media or an amendment. These are great for ebb & flow, aeroponics, deep water culture, or a drip system. This is a very clean product that allows for easy drainage. It is best to keep your watering on a timer so that it doesn't get too dry for too long.

Perlite ~ rarely a stand alone media, it is used more as an amendment to soil and coco fiber to aerate the soil and allow for better drainage.