I'll probably get flamed with "repost" or something for this, but hey, I've been lurking around here for about 1½ year, so it's time to atleast try to contribute
So here goes nothing.
In the north eastern corner of Storm Peaks there is a cave full of a mob called Wailing winds.
They drop crystallized fire at a fairly good rate, but the real awesomeness of this place is the respawn rate, as well as how desolate it is.
Been farimg there from time to time for over a week, and I think I've met someone there 3 times, and even then there's been plenty of mobs for us both.
Link to the mob on wowhead
Wailing Winds - NPC - World of Warcraft
This might be commmon sence, Hell I dunno, But I've been racking up above 15 eternals an hour here, and It's been a great source of gold since the WotLK release, so I hope It'll atleast help someone ^^
Edit: Typo