Every type of sub-bending in Avatar: The Last Airbender
Earth:
1. Metalbending
One of the coolest types of bending in Avatar has to be metalbending, which involves the earthbender locating and manipulating the tiny traces of minerals still present in a refined piece of metal. The young earthbender Toph single-handedly develops metalbending when she's held captive in a metal cage by Xin Fu and Master Yu.
After the Hundred Year War, Toph founded a metalbending academy outside the colony of Yu Dao. After Yu Dao became part of the United Republic of Colonies, Toph became the city's first chief of police, and her force mainly utilized metal bending to keep the peace. Her officers are equipped with metal cables that they use to apprehend foes or swing around Republics city, Spider-Man-style.
Other prominent metalbenders include Toph's children Lin, who became the United Republic's chief of police after her mother, and Suyin. Suyin even founded the Metal Clan who dwell in the city of Zaofu, which is constructed completely out of metal.
2. Sandbending
Since sand is made up of micro-sized grains of earth, some earthbenders are able to bend sand. This ability is mostly found amongst the natives of the Si Wong Desert in the heart of the Earth Kingdom, where numerous tribes of sandbenders live. Although seemingly any earthbender can manipulate sand, those who live in the desert have an easier time after years of practice.
The sandbenders travel around the desert in boat-like sailers that they propel by whipping up a localized sand storm.
3. Lavabending
A very select few earthbenders are able to summon lava from underground or even melt rocks down into liquid lava. Once the earth is in liquid form, the bender can morph it, similar to how waterbenders create ice weapons. For example, we see the lava-bender Ghazan bend lava into a spinning blade to cut his way through a prison cell.
In addition to Ghazan, the only other non-Avatar we see utilize lavabending is Korra's friend Bolin. In a flashback, Avatar Szeto used lavabending to cause four different volcanoes to erupt simultaneously. While manifesting himself through Aang, Avatar Roku used lavabending to destroy his own temple and save Aang and his friends from capture.
Perhaps the most impressive feat of lavabending was when Avatar Kyoshi broke an entire peninsula of land off of the earth kingdom to creat Kyoshi island.
4. Seismic sense
Seismic sense is the ability for an earthbender to sense the vibrations in the ground and make a 360-degree mental image of their surroundings. This ability was developed by the badger moles, who used it to navigate underground passages since they lack the ability to see.
Toph was the first human to learn this ability when she ran away from home. While she was crying in a cave, a group of badger moles found her and she was able to connect with them through seismic sense since both parties were blind. Toph constantly uses seismic sense since she is blind and she got so good at it that she could recognize people by the way they walk and even tell if someone is lying by sensing their physical reaction.
Toph taught this ability to Aang as well as her daughters Lin and Suyin, making the Beifongs arguably the most powerful earthbending family to ever exist.
5. Glassbending
The Avatar Kyoshi books confirmed that glassbending is possible in the Avatar world, which makes sense since glass is made primarily of sand. During a fight with a street gang called the Triad of Golden Wing, Kyoshi removes shards of glass from her skin by bending them.