Hey, Now leveling mining on my horde char, and Nethergarde Armory in Blasted Lands is really nice for it : lots of mithril, small thorium and if you`re lucky even a rich thorium vein. What makes this place special for Alliance, is that the mobs there are friendly to Alliance. So if you are tired of running around random spots searching for veins and tired of fighting off random mobs to get to the veins, this is your chance!
Oh, forgot to mention that the entrance to Nethergarde Armory is a bit NW from Nethergarde Keep. If you`re coming in from Swamp of Sorrows, just stick to your left and it`ll be easy to spot.
.Edit : Ah well, seems it does not work for Alliance, but still it`s a great mining spot, chopping 3 stacks of Mithril and a stack of Thorium each hour.