Edward Castronova, the economics professor who estimated that the GNP of Norrath, the setting of Everquest, is higher than that of many developing countries, has now determined that male Everquest avatars are worth more real money than female avatars:

"[...] ability seems more important than sex in determining the value of a body. Nonetheless, among comparable avatars, females do sell at a significant price discount."

(From BoingBoing.)