Tailoring is the cloth armor crafting profession and with three classes wearing cloth armor in classic the potential is huge. On top of that healing gear and spell power gear can be the best options for caster and healing hybrids, so add druids, shamans and paladins to your potential list of clients.
Spellpower is king
Spellpower is by a significant margin the best stat for casters, and in classic it is not particularly abundant. This is doubly true for low level gear, where spellpower is almost non-existant. To shore this up Blizzard has added some new spellpower recipes for tailoring, and they are pretty good.
World drop recipes
There are a lot of world drop recipes for spellpower of various types. All of these are very good for various casters. In addition Blizzard just added two new vendor recipes that give spellpower with the Invoker pieces. This means Silk has taken a short term massive increase in price, but longer term this should be stable.
All of these recipes are Pre-raid BiS or better and are well worth keeping in stock. The Phoenix gloves and Pants are quite expensive, requiring an Iridescent pearl, and the Hands of Darkness require shadow protection potions. The other pieces are relatively cheap and requirer cheaper materials in addition to the cloth.
Here you can grab my TSM group to restock and post these to the Auction House. As usual it will only work if you actually know the recipes. Good luck and happy hunting!