Dracolich

Dragons live a long time, but they still die. Dragons can choose not to and use dark rituals and unholy pacts to consume themselves. They bind their souls to a precious gemstone 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 mouldier or skeletal. 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 utterly dominated dragon guard wights?

In Pathfinder, they're a lot nastier; called "Ravagers" (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.