Auction giant eBay has disallowed the buying and selling of World of Warcraft currency. But if you want to buy your way into the upper echelons of the game, you still can: Head over to Sparter, an online exchange for WoW gold (and also currency in EverQuest and Eve).
Sparter is not an auction site like eBay is. Sparter enables the trade of just one type of item (so far), and prices vary depending on lot size (how many golds) and how quickly you want them delivered to your account. Sparter escrows the transactions, so you're not charged until the currency is delivered to your account. Like eBay, however, there is a reputation score that gets attached to sellers.
Here at CNET, dedicated MMORPG players have mixed opinions about the concept. While the Sparter market looks to be more gamer-friendly than IGE, the very concept of enabling players to buy virtual goods rankles more than a few people. World of Warcraft terms of service prohibit the "real-world" sale of in-game items, and many gamers think it'd be better if real-world transactions were more actively quashed. For more, see the News.com story, eBay bans auction of virtual goods.
Currency in Second Life, by the way, remains for sale on eBay and is not for sale on Sparter.