Although they just dropped a way of buying game time with in game gold some people may still want to pay for game time instead of spending their in game gold. I personally would recommend the website G2A.com for buying game time, you can purchase 2 months of game time for the cost of slightly more than one month at Blizzards prices. I can confirm this website is legit as I have used it a lot for game time in the past.
Good tip, assuming the site is indeed legitimate. WoW is going the wrong way in allowing users to buy game time in gold, though it's not like we use gold for much in the game. I have a stockpile/vault of gold, and I don't really spend it on much in game, but some people throw their gold at certain uses.