Grinding Feral Scar yetis in Feralas took me from 45-47 and netted me about 500 leather, TONS of grays (which vendored from 20s-1.5g), at least 40 greens, and at least 10 blues, along with food/drink and mana/health pots. Drop a combo of heavy/thick, and not a lot of hide (thank god). They spawn fast, are spaced pretty far apart so little extra agg, pats are singles. 43-46 range and they fall easily. Did this with a rogue, no need for stealth, didn't even bother to waste poisons. Solo got about 210-270xp per, half that with a pally with me who was there to mine iron and mithril. I recommend doing the duo thing with a miner just cause you can clear the caves in pretty short order, every one gets mats, and its nice to have company :). On Balnazzar this is not a heavily played spot, would see horde occasionally, everyone kept to themselves. Someone told me they think Feralas may have some kind of xp bonus, don't know how likely this is but possible. No chests dammit but drops are nice enough. Lower level yeti cave is south of the road, a little west of Dire Maul. There is a higher level yeti cave (47-49) just east of the road goign north from the road to the Feathermoon boat. They drop rugged but same xp :( and fewer of them, which means you clear the cave and sit and wait.
For med leather (which I grind for gob engin. guildie) the yeti cave in Hillsbrad is good, but Horde heavy so if you are on a PVP server either go in a pair or try to hit it when there aren't a lot of people around.