Suicide

Committing suicide by using a self-damaging ability to kill your character counts as a player-caused kill and does not have the -10% durability penalty attached to it.

This does not apply to dying from a hazardous environment, such as standing in fire, swimming in lava, or jumping off a cliff.

Suicide by spells/skills

 * Hellfire: a warlock spell.
 * Shadow Word: Death: Dying from this priest ability will not reduce the caster's durability.

Suicide by items

 * Dark Rune: an ingredient used in some professions.
 * Demonic Rune: an ingredient used in some professions.
 * X-52 Rocket Helmet: dying from the damage received upon activation of the X-52 Rocket Helmet won't reduce durability, however death by falling damage after it has been activated will.

Former methods
These spells and items have been removed from the game, but they were useful to avoid a durability hit in case of emergency.
 * Divine Intervention: when protecting someone with this spell, the paladin automatically die. Ability removed in Patch 4.0.1.
 * Seal of Blood / Seal of the Martyr: paladin spells. These abilities were removed in Patch 3.2.0.
 * Skull of Impending Doom: a quest reward. No longer obtainable as of Patch 4.0.3a.
 * Videre Elixir: used to kill one's self at the Gadgetzan graveyard for the quest Meet at the Grave; the is a ghost who's only visible to dead players. No longer obtainable, as of Patch 4.0.3a.
 * Crystal of Zin-Malor: an Alliance-only item. Ideal for canceling flight paths. This trinket will drain health and mana until the player dies or unequips it. No longer equipable as of Patch 3.1.0. Quest chain also removed, in Patch 4.0.3a.