Sorry for the late post, hectic day at work (again), and class afterwards. Anyway, ON WITH THE SHOW!
Old content: MC, BWL, etc. It's still there, it's super easy, and you can get it done quick. Why?
1.) BoE Epics. These won't sell for a lot, considering players are going to be constantly trying to level and get BETTER gear. However, they will drop a few hundred gold on them. Mostly look for DPS sets; BoE epics from level 60 content is usually more towards putting classes into neat little boxes - priests are healers, warriors are tanks, and so on. Rarely will you see a warrior try to dps in tank gear.
2.) Crafting mats. If you go to MC, some very popular items that will drop are:
Essence of Fire: One of the more common ones, and one of the major ingredients to Fiery Weapon, a non-level requirement enchant which is quite possibly the best one at that level.
Lava Core, which is used for reputation grinding for Thorium Brotherhood. If you're like me, you like having Exalted reputations, so there is a niche in this market, both on the buying and selling end (okay not technically a crafting material but whatever).
And of course all the regular mats, like the cloth. Uncommon items to sell on the Auction House or disenchant as well drop quite often.
3.) Cash drops. Magtheridon has a wealth of 500g. At level 85, you may need another person or two, but the whole instance should take less than 10 mins including travel time. That's 1002g per hour, approximately, discounting the epics that may very well vendor for upwards of 10-20g each.
There you have it. Now go nostalgia it up and clear some old content for fun and profit!