Rugged Leather

If you are lvl 70+ I suggest trying Dire Maul North. Just tag all those mastiffs from first two rooms and aoe them down. I got around 80 rugged leather/run. Good luck.

I read some other posts (didn't see any here so wanted ot be the first one) and found that the Yeti's in winterspring were a good source of rugged leather, but I was getting thick leather and thick hides as well which I didn't need for leveling my leatherworking. This is now a level 50-55 area so after looking at the other areas it looks like Blasted Lands and Silithis would be the best place to skin to ensure a 100% drop of rugged leather. I think this is a big deal mainly because ever since the new expansion all I have been able to get when I skin is one piece of leather at a time which is different from the 1-3 you could get before. I though it was just for savage leather, put apparently Blizz nailed it across the board so if you need 300 pieces of leather you actually have to kill 300 mobs to get it unless your in a guild with the Bountiful Bags perk (which unfortunately my horde toon is not). I think this is kind of crap considering that with mining and herbalism you can still get more than one piece of ore or herbs even without the guild perk.
Silithis- Checked WOWhead and the drop rates are higher for rugged leather (about 50%) than thick leather (41%), but I ended up with more thick leather than rugged after 15 minutes.
Blasted Lands- I went to the tainted forrest and the drop rates for rugged leather are higher, I killed tainted bears as they have fairly low health and they drop bear flank so if your still leveling your cooking then this comes in handy. The tainted screechers drop rugged leather primarily as well. Only draw back is the tainted nightstalkers aren't skinable, and they don't drop anything really useful.
Winterspring- I got more rugged leather than thick, plus they drop money and runecloth

The Blasted Lands is the place to go for rugged leather. There are skinnable creatures wandering all over the place-boars, basilisks and hyenas. All these drop mostly rugged leather when you skin them-I found the drop rate to be well over 95% with just a few thick leather thrown in.