2 different methods! (although one takes a lot longer)
1)If you die somewhere where you cannot get to your corpse (high in the air on one of the floating islands, etc) ressing at a spirit healer is very expensive (especially if you carry around multiple gear sets.)
However, if you get a friend to party with you and queue you for all Battlegrounds, you can join the battleground while dead and then /afk out to res for free! (you can even beg some mana biscuits / buffs off other players first)
I did a search and didn't find this. Its something I have known for a long time, but not everyone will know and it saves you a lot of money!
(You can join battlegrounds while dead, while you cannot accept a summon. No idea why they designed it that way but they did!)
2) Walk into a capital city, and log out. Wait about 12hours, when you log in again you will be alive! You don't have to walk into a capital city, but it will take a lot longer if you don't. (I think it uses the same timings as getting rested XP, since its seems to go faster at the same rate in a capital city. A normal inn will not work as you do not get the "resting" Zzz icon while dead in an inn, but you do in a capital city.