there used to spawn 2 drakes and one dragon in Tram.
I don't know about fel - is sadiva there too? But then it's not that easy to get there in fel unscathed, so probably not worth trying when hunting for leather.

Easiest place to get leather w/o work is Destard (on ATL shard at least) It can get pretty busy in there, but losts of dragon/drake/wyvern corpses to loot from. Just hand out in there with a beetle and two bonded packys outside and you should get some decent amounts in no time

Giant serpents on Valor Isle also give bones [in addition to spined armor:]

any gaint serpent can give bones, zombies also shadow wisps in ilshenar give bones.

Nightmares can also be hunted for barbed hides.
They are quite a bit easier to kill than dragons.

In Felucca nightmares give 20 hides each, which is easy farming if you don't mind dodging the occasional PK from time to time.

For me the easiest place to kill drakes is fire temple, just lure them out a few at a time, whack them and head back in.
Not sure if greater dragons spawn there now though...

Greater Dragons do indeed spawn at the temple.

I had one teleport from the room underneath onto the stairs right in front of me. Nice.

Nice, another good spawn turned into slaughter fest!

By the way, nice tip of the nightmares... I didn't think of them!

Not really. I spent 2 hours at Demon Temple a couple days ago. I stayed up top killing demons and had not issues with the greaters. Made a killing so to speak.