Over at the Official WoW Website, Blizzard has put up a couple of pages detailing which items have been created by players the most, which items are auction house bestsellers, which mob has killed the most adventurers, which items have been gathered the most, which items are frequently acquired by looting and which quests have been completed the most by players.
The Cloth and Leather family’s strong showing in both in sold and created categories isnt a surprise as many recipes require those materials. Same with the starting quests being the most completed by Players. Although i wouldve throught Onyxia would be 1 or 2 in the most kills category but slid down to 3rd. It is a daily ranking so things may change.