what about two gathering professions? Mining and herbalism?

This is a rather hard question to answer because it's all based on your servers economy. Gathering professions are a nice starter, but once you get into high level raiding and daily quests you start to unlock patterns for Primary professions that can guarantee a lot more money than the gathering professions if you are willing to work for it.

herb and alchemy

Herb and alchemy. Stick with them. They're boring at the beginning but when you get higher. You'll have a TON of gold I guarantee it.

Yep, as they said. sell enchanting mats. but it is slower than two-gathering professions. for example, Mining and herbalism.
If you want to make gold use non-gathering profession, it is not a best choice.
Best way to get gold IS farming.. but also have two gathering professions..such as skinning / herbalism etc. You can sell that stuff for a ton of gold.
Also, consider getting an add on mod for the auction house.. helps show who is undercutting items..buy those and then resell for an 'average amount.' I buy that stuff and can make several hundred gold just from being a wise buyer in the auctions.
Lastly, stay out of the auctions as much as possible until you are level 85. don't waste it on low lvl garbage.
Above all, if you have no time, just buying online. i'd like to recommend to you a site which my friends recommend to me. GOOD luck.
http://www.guy4game.com/world-of-warcraft-us/wow-gold/?aid=1891
Hope can help you, my friends