How much gold you make depends solely on your server.
I play on 3 different servers (2 pvp and 1 pve)
What you are farming: Essence of Undeath (For some reason these sell for anywhere between 8 - 15g a piece on the servers i play on)
What you are killing: Infected Mossflayer They seem to have the best drop rate for this.
Just walk over the graves to spawn them. Any level 60 - 80 with any kind of aoe could easily take all the graves out in 15 seconds.
Location: Eastern Plaguelands
Unfortunately the graves only respawn every 5 minutes.
You can kill the mobs in the area for an additional 20g an hour while you wait for them to respawn. Or you can have a smoke, grab a beer, or browse the internet or whatever you do when your not on wow.
Also if you have Mining/Herbalism/Enchanting you can make a little bit more.
Miners - A few Regular and Rich Thorium Nodes (2.5g a piece of ore on my servers)
Herbalists - A few plaguebloom herbs around (2g a piece on my servers)
Enchanters - I picked up 4 greens in the hour i was there. (DE'd into illusion dust x5 @ 1.5g a piece)
I tested this on 3 servers and this is my average.
Grays and Pocket Change = 25g
Runecloth = 40 - 50g
Essence Of Undeath = 200 - 220g
Total Earnings = 205g - 295g
I'm sure Miners would profit the most. Also keep in mind this is for people who don't feel like doing alot and are playing while they are talking on the phone or playing xbox or something.
Please save the whole "200g an hour isn't much" comments.
To those of you it helped, Your welcome.