Ok for some reason I'm getting a lot of Google hits by people looking for places to farm Borean Leather in Northrend, I'm not quite sure why, since I haven't talked about skinning much, but I'll quickly address it here.
First off, why are you people even searching for this? There are so many things to skin in Northrend. If you'd been looking for Saronite or something, that would've been understandable. Well, I guess Leatherworking takes a lot of leather to level up.
You should be able to get a lot of leather just by leveling through Northrend. If you start in Borean Tundra, right off the bat you can grab leather and Nerubian Chitin from the things skittering around Warsong Hold, as well as Arctic Fur (I'd like to point out that Arctic Fur has a random chance of being skinned off every mob). In fact by the time you leave Borean Tundra, your skinning should be pretty much maxed, owing to the Nerubeans, the odd wolf or Caribou and the plethora of mammoth roaming the Tundra. Since killing the mammoths isn't directly a quest goal, and they travel in packs, it should be easy to kill a bunch and skin them (even Rogues, Shamans and Feral Druids will get AOE in the next big patch). Just stay away from the D.E.H.T.A. if you're on a skinning spree.
If you started in Howling Fjord, then there's Shoveltusks and a few wolves to skin as you quest, but mostly you'll be fighting Humanoids so the pickings for leatherworkers are leaner than the Tundra (much better for cloth though).
Grizzly Hills is also good for skinning, but Sholazar Basin, for those high enough, really stands out for Leatherworkers. Most things can be skinned, and there's also Drakes for Icy Dragonscales. Additionally, in the Basin, the mobs are high enough levels that you won't be skinning scraps.
If you want to try something else, you can get a decent amount of Leatherworking materials from running instances. Violet Hold is good for Icy Dragonscales and Borean Leather, and Azjol'Nerub is great for Nerubian Chitin. Since you'll probably be running stuff with at least two DKs you have a decent chance of being the only skinner, and if you're a Druid or Shaman then the fact that everybody in Northrend is looking for a healer means you'll have an easy time finding groups (tonight during a two hour session there were two groups "LF Healer Utgarde Keep" in Howling Fjord).
I hope that helps all you Skinners who have been directed to Udder Madness.
A Shocking Display
8 hours ago