Dracolich

Dragons live a long time, but they are still mortal and, one day, they will still die. Some dragons, however, choose not to die - they use dark rituals and unholy pacts to consume themselves. They bind their souls to precious gemstones, and take on many of the properties of a lich.

Due to their innately evil nature, dracoliches tend to be of chromatic dragon stock, and look mostly like they did in life - just, y'know, more skeletal and/or mold-covered. Dracoliches retain all of their living abilities (like breath weapons, flight, frightful presence, and so on), but gain all of the usual undead immunities and vulnerabilities (poison, charm, paralysis, etc.). Most DMs will also throw in the ability to control undead too; they are a Lich after all, and what self respecting undead dragon lord doesn't want an entourage of dragon guard wights?

One important difference between a dracolich and a regular one is that a dragon's body is too magically-potent to just regenerate around the phylactery: the dracolich's undying soul needs a fresh dragon corpse to possess in order to have a physical form if its body is destroyed. This means most of them locate their phylacteries near sources of other dragon corpses or hunt up more when they're running low, both providing a number of cool campaign hooks and giving their lairs a sweet "dragon graveyard" motif.

In Pathfinder, they're a lot nastier; known as "Ravener" here (because Dracolich is trademarked), they're soul-eating monsters who pretty much exist to fuck shit up.

Most important in the Forgotten Realms; the Cult of the Dragon, a crazy cult headed by an uber-crazy lich named Sammaster, goes around creating dracoliches because they want to fulfil a prophecy in which dracoliches will conquer the world. Why? Um... mostly because Sammaster wants to prove that he translated the prophecy right and everybody else, who says it actually reads as a prophecy about dragons taking over the world after a great apocalypse, is wrong.