Herbalism is far better than mining. People use potions like crazy, far more than they use minerals. But don't take both mine/herb cos they share the same minimap.

After herbalism pick up skinning (recommended for warlock/hunter) or enchantment (recommended for rogue/shadow priest). Skinning early on is so-so money, but when you reach 60 you can skin dragons and devilsaurs for good money. Hunters and warlocks are good for kiting those reptiles. If you shadow priest/rogue you can farm instances by killing the sub bosses and disenchanting their greens/blues.

When you have enough for epic mount + 200g, Dump your skinning/ench for alchemy. Use the 200g to up your alchemy to 300. Ever since BG came about, potions sell like f*ing crazy. Trust me.