There are Demonic Runes and Dark Runes which exchange health for mana. (e.g. Restores 900 to 1500 mana at the cost of 600 to 1000 life.) Spell Description (used by both runes): http://thottbot.com/?sp=27869
Demonic Rune:
Dark Rune:
The idea is to use the rune when you have less health than the rune restores. If you have 580 health left and you pop a rune you will kill yourself because it takes at least 600 health. When you kill yourself in this fashion you avoid the damage your equipment would otherwise receive. Melee and caster classes can both use these runes. This is particularly useful in raids when you are expecting to wipe... you will rack up little to no repair bill with this method.
Although Dark Runes are expensive on the AH they may cost less than your repair bill, you decide. I would suggest farming demons in Felwood or Azshara for their high Demonic Rune drop rates.
~Leoj:yuck: