Generated Structures

Generated Structures are structures that naturally spawn in a world.

Mineral Veins
Mineral Veins are generated structures that contain Ore. They spawn underground and can appear anywhere where there is stone.

Dungeons
Dungeons are underground structures that consist of Mossy Cobblestone, Cobblestone and a Monster Spawner which can spawn Zombies, Skeletons, Creepers and Spiders. They contain rare and valuable loot.

Villages
Villages are above-ground structures with houses, farms, etc. They almost always contain Villagers. Villages often have blacksmiths. There is always a chest with items inside. Some villages' blacksmiths burn down before the player can get to them.

Desert Wells
Desert Wells are naturally generated structures found in Deserts. They carry an infinite source of water which may be helpful due to Deserts usually containing no water sources.

Strongholds
Strongholds are sometimes above-ground and sometimes below ground. They are large, having many wings, rooms and halls. They contain the "portal room"—the room in which an End Portal is located.

Lava Pools
Lava pools are small pools of Lava that spawn randomly in the world. They are less likely to generate than regular water pools.

Moss Stone Boulders
Moss stone boulders are generated structures that spawn in Taiga Biomes. They are very rare to find.

Ice Spikes
Ice Spikes are generated structures made completely out of Packed Ice. They only spawn in Ice Spikes Biomes, but are very rare. Recommended to use seed to find them.

Abandoned Mineshafts
Abandoned Mineshafts are small mineshafts, with randomly generated Rails. They are often connected with Caves. They contain Cave Spider spawners. They do not contain chests yet.

Caves
Caves are openings in the surface that lead underground. They often contain Dungeons, Abandoned Mineshafts, and rarely Strongholds.

Libraries
Are structures with bookshelves in majority. Can only be found in strongholds and villages.

Glowstone Cluster
Are naturally spawned structure that is composed of mainly glowstone. It is found in the ceiling of the Nether Dimension. They are the only way to obtain glowstone in Survival.

Nether Fortress
Complex fortresses comprising of Nether Bricks. Contain chests containing valuable loot. Blaze and Wither Skeletons spawn in these.

Trivia

 * Before Update 0.11.0, Abandoned Mineshafts contained Spider Spawners and not Cave Spider Spawners.
 * Before Update 0.9.0, there were no generated structures (except Mineral Veins).
 * Caves, in extreme cases may count as an exception, as they can sometimes generate in pre-0.9.0 seeds such as nyan.
 * Generated Structures such as dungeons, strongholds and spawner rooms may sometimes contain chests with loot.
 * Ravines were planned for 0.9.0, but were not implemented.