People buy mats to powerlevel professions, they're the new reroll. (Actually, it's always been like that). From what I see on my server, nobody wants to spend one second more in Outland than they have to, and will buy mats from those levels for good prices.

Older enchants can still sell, too - Mongoose sells for 400g on my server, all you have to do is grind the mats, or buy them cheap when they show up.

Perfect gems are a good market too - because gear is so easy now from badges, I see people commenting a lot in Trade to just buy perfect gems for blues and AH/Crafted epics, don't waste money on epic gems until you get badge gear.

Cooking is a good steady source of income.

People are lazy. Write that on a sticky, and put it over your monitor, it's your motto for playing the AH. So many players have piles of gold, that they're willing to spend on things like professions, pets, and gear for alts. The Heirloom gear has had an effect, but the older stuff does sell - especially tailoring.

And yes, it should be said again - bags, bags, and more bags. They sell.