I know this type of post has probably been posted a thousand times before, but here's mine.
I have 3 max lvl engineers, 2 max lvl transmutation master alchemists, one max jewel crafter, 1 max enchanter, 1 max tailor and a max herbalist and miner.
Here is what I have been doing with the professions. I'll list them out and if anyone has any better ideas or things to add that I might be missing I'd be greatful for the advice.
My 2 alchemists are transmuting the living steel CDs daily and making trilium bars.
My 3 engineers don't really do anything, however, next patch I will make 3 of the new mounts. 1 for myself and 2 to sell.
My enchanter currently just DEs PvP gear for the Sha Crystals and sells them.
My tailor makes frostweave bags and sells them.
My herbalist herbs and miner mines. I've been sending the Ghost Iron Ore to my alchemist to turn into trillium.
My jewelcrafter i just leveled up to max so I'm not really sure what I should be doing to maximize profit from them. Should I just be prospecting ore and start sending some of that ghost iron to them?
Windwool should be plentiful and cheap. On my server it is nicely profitable to buy Windwool for 20g or less a stack, use Tailoring and 1 of the 5.2 discovered PvP recipes that use 4 bolts (= 20cloth) to make a PvP item that your enchanter can d/e for an Ethereal Shard. Ethereal Shard go for 25g+ on my server. Bonus points if you are in a level 25 guild with the Bountiful Bags perk and get more then 1 Shard from d/eing sometimes.
I use it only to make cheap shards for myself that I turn into a Sha Crystal each day with Enchanting cooldown. Not even taking extra shard procs into account that means I turn less then 100g worth of windwool into ~225g worth of Sha Crystal (or more accurately the high end weapon enchants you create with them, cause those are easier to sell then the Crysals.)
Depending on your server's prices this may work for you as well. It's not much, but it takes hardly any time to do so it's a decent way to spend time on professions.
If you have that many toons (most likely max level) then farming on Sunsong Ranch can be a profitable venture as well (for the time invested each day). If you don't need Spirit of Harmony for your toons professions I can recommend planting Enigma seeds and getting Golden Lotus + herbs. Those can then be used in a ton of different ways to make gold with your professions. When doing this for a while I turned the herbs into potions, and the Golden Lotus I used to transmute Rare gems (Orange only in my case). Transmuting meant it was usually about 35-40g extra profit then I could have gotten for the Golden Lotus alone. I churned out more Lotus then I could transmute and sell though, so I ended up selling Golden Lotus straight as well.
It's not big profits by any means, but done with several toons it's a constant extra gold income for just a few minutes of work.