(1) EpicToon - EpicToon is a gold company that has only been around for a few years now but during that time it has been a good example of what an online currency game site should be. The prices that they sell gold for is good, not as BankofWOW but very close. They have outstanding customer service and good delivery times.
I highly recommend this site as a good place to buy WOW gold. I have nothing bad I can say about them and I highly recommend them.
(2) Bank of WOW - Bank of WOW is a gold currency site that focus's only on selling gold for World of Warcraft and no other game or service. They offer some of the best prices on WOW gold you will find. This is a highly specialized company and they have a good reputation. If you are looking to make a large gold purchase and want to get the most bang for your buck I would suggest going with them even if it takes a little longer to get your order.
(3) IGE - IGE is the oldest and largest gold company out there. It has a very good reputation now, years ago it did not. I now recommend this company as a good place to buy gold for WOW or currency for other games. The only negative thing I can say right now is the price is a little higher with IGE now that it is when compared to the other companies I list. Price is not everything though IGE delivers in the customer service and delivery time area.