Sometimes I read tips in blogs or on forums & jot it down to try/look into later. This is one of those tips that got buried in the snowfall of paper notes on my desk but I spilt my coffee this morning & had to do a rescue mission (oops!) so this one, quite literally, floated to the top!
Leather - yes, just boring old Borean Leather or Savage Leather - it appears to work for both which is rather nice if you're levelling a skinner through Northrend at the moment :)
I've had a look on 2 different servers for these prices and they vary wildly so it's not a guaranteed money maker but it's worth a look on your server.
Server 1 - Savage Leather 4.5g (x5=1 heavy @ 22.5g) (x50=225g)
Server 1 - Heavy Savage Leather 23g (x10=230g)
Server 1 - Pristine Hide 300g
So it doesn't matter whether I buy Savage or Heavy Savage Leather - when I hand in 10 Heavy Savage Leather to get my Pristine Hide (at the Twilight Highlands leather trader) - my profit here will be 70-75g.
Server 2 - Savage leather 4g (x5=1 heavy @ 20g) (x50=200g)
Server 2 - Heavy Savage Leather 39g (x10=390g)
Server 2 - Pristine Hide 340g
But look at this! Server 2 has a much wider discrepancy - my only choice here is whether I can sell 10 Heavy Savage Leather to make profit of 10x19g or I go for slightly less profit but only have 1 item to sell (and by the looks of it, a scarcer commodity, less competition so I could perhaps push prices up a little).
Obviously the Savage -> Heavy Savage conversion only works if you have a Leatherworker (or access to one, of course) but if the prices work in your favour, it may be worth a visit to the trader in Twilight Highlands. I've also seen (& bought!) stacks of Savage Leather Scraps for 11g a stack - that's 2.75g per Savage leather when converted, so it's worth keeping an eye on those too.
I actually don't do this very often - I've been popping over to Tol Barad for the 'virtually' free leather there from skinning the crocs that everyone is killing for the daily. I say virtually free because it costs me time but I can pick up 10 Heavy Savage leather in less than 10 mins on a good day & 20 minutes on a bad day so it doesn't even cost that much time! Add in the Strange Bloated Stomachs & Crocolisk Tail which I cook & sell, it's a pretty good little earner.
Now at the beginning, I mentioned Borean Leather - same principle - 5 Borean Leather Scraps = 1 Borean Leather, x6 = 1 heavy Borean leather
Server 1 - Borean Leather Scraps 0.15g (x5=0.75g) (x6 = 4.50g per heavy)
Server 1 - Borean Leather 1.2g (x5=7.2g per heavy)
Server 1 - Heavy Borean Leather 14g
Server 2 - Borean Leather Scraps 0.65g (x5=3.25g) (x6 = 19.50g per heavy)
Server 2 - Borean Leather 2.0g (x5=10.0g per heavy)
Server 2 - Heavy Borean Leather 17g
On either server, profit from converting Borean Leather to Heavy Borean Leather is around 7g, scraps prices can vary wildly so on a good day, you may get server 1 prices!
Once you've got used to doing the quick maths in your head, you'll know at a glance whether it's worth going for on any given day - the other items to remember is the Mammoth Mining Bag & Trapper's Travelling Pack - both take 8 Heavy Borean or 48 Borean Leather - but they usually sell for around 200g on server 2 so it's not often that I ever sell Heavy Borean Leather as it is, there's better profit in the bags for me.
Besides, a girl can never have too many bags, can she? lol