Astral Recall is a level 44 shaman spell that works identically to a [Hearthstone] but is on a separate cooldown and does not take up any inventory space. It teleports you to whichever settlement or city you have previously designated as your home.
Astral Recall works as a second Hearthstone and will teleport you to wherever your Hearthstone would take you. It is not possible to set up a separate home for Astral Recall, meaning the main use of this spell is to allow you to return home more frequently. Unlike your Hearthstone it cannot be used in combat, but being a spell it benefits from haste and will thus be slightly faster than using a Hearthstone if you have any haste on your gear. You can also use temporary haste bonuses like [Bloodlust] and [Berserking] to further reduce the casting time. Coupled with the level 72 ability [Spiritwalker's Grace], Astral Recall can be cast by Restoration shamans while moving or falling. Note that you still need to be out of combat to use Astral Recall, severely limiting its usefulness for escaping from bad situations.
You can destroy your Hearthstone to free up an inventory slot. You get a new one by visiting your home inn or setting a new home, meaning that you can pick up a new Hearthstone immediately after using Astral Recall if you anticipate having to return home again before the cooldown period is over.
If you are a troll, you can make a macro that uses Berserking right before Astral Recall, allowing you to return home a few seconds sooner. Since you're unlikely to need Berserking in your home town, there is rarely any reason to not use Berserking in this way, but it saves you the time and effort of having to remember to click Berserking any time you want to use Astral Recall. A similar macro can be made if you have any on-use haste trinkets.
Patch 7.0.3 (2016-07-19): Cooldown reduced to 10 minutes, down from 15 minutes.
Patch 1.3.0 (2005-03-07): The tooltip now includes the home point the spell will recall you to.