Earthbenders have the ability to manipulate anything made of earth (rock, sand, clay, stone, coal etc) in several ways. They can "rip" chunks of the earth from the ground and control its movement by slinging or sliding it at an opponet, or gracefully hovering it in mid-air. They can also raise a solid rock wall from the ground to block an opponent's attack. The other way they can manipulate material made of earth is to change its consistancy from solid to sandy which is typically used in a defensive move. As an opponent is coming at them, he may find the solid earth beneath suddenly turns to quicksand and he sinks. The Earthbender can then change it back to a solid effectively trapping his opponent.
And extremly rare form of earthbending also exists: "metalbending", the ability to bend processed earth (ore and metal). It is so rare that only one person within the Avatar world has been shown capable of mastering this artform.
Hong Gar style of Martial Arts
The movements of Earthbending are based on the Hong Gar style of Chinese Kung Fu a style known for its strong stances like the horse stance (legs apart and knees bent into a low position of gravity). This stance helps to root the Earthbender to the ground. Their movements are often based on the movements of animals, particularly the tiger and the crane which combines both power and speed. Tiger movements provide the raw brute power (hard power) to overcome an opponent. Their hands movements mimic that of a tiger's claw as the Earthbender "rips" chunks of earth from the ground. The crane movement on the other hand is softer but faster allowing the Earthbender to quickly erect a stone wall in front of him or sweep objects rapidly at an opponent. Earthbenders use the Hong Gar style of Kong Fu to tap into the emense power of the planet making them an admirable force to be reckoned with.
(Thank you BakaNeko for the link)