My "main" is JC/Tailor and my Mage alt is Engineer/ Enchanting.
I will be ditching the main for a Monk and keeping the Mage as my alt This will allow me to cover Tank, Healer, MDPS and RDPS. Enchanting is such a money saver when you get to DE your old epics for crystals to enchant the new epics and Engineering is a lot of fun, as well as providing a "burst" CD (480 of X stat at the moment, I presume this will be upgraded to MoP level).
It seems weird for my Monk and Mage to have the same professions and I wouldn't mind an Alchemist. So maybe Enchanting and Alchemy? Money saving and provision of raid buffs. My main annoyance with this is that I have levelled every profession several times on my 9 level 85s (boo @ my 73 Hunter) and dropped professions several times. I miss the days when all my characters were on the same realm, providing a good network :'(