Cloth has always been a farming staple. It doesn't require any special skills, and you can begin right out of the gate. Changes to the game over the past year have put some cloth in even higher demand, making it an incredibly lucrative business.
While any cloth is worth farming, there are two types in particular, wool and mageweave, that fetch a high price. This is because, compared to the other types of cloth, they have a short window of appearance when leveling. Depending on how often you linger when questing, you practically jump straight from linen to silk, and from silk to runecloth.
To add to this, Blizzard has increased the speed at which we level, and even added bind on account shoulder armor that speeds us up even more. You can even Recruit-a-Friend for an unprecedented bonus.
The advent of achievements has also increased the demand for cloth, as people are eager to earn reputation, become pirates and then buddy up to the goblins again, and maximize professions. So how can you best take advantage of this market?