I have used Tusongame.com to buy gold for many different characters on several servers, they have always been the cheapest and always delivered although sometimes the delivery does take a few hours when they are short on gold.
The website itself only seems to work perfect in Internet Explorer, I have trouble viewing it in Mozilla Firefox.
The customer support is not very helpfull at times as they do not speak or understand english very well. For Example: With the gold they also send you a standard message in the mail (very bad english, does not make alot of sense) and when I bought 500g for a friend's christmas present they did not understand that I wanted the in-game message to be different.
Very reliable, Very cheap, Never had any problems with them, The first place I go when I need to buy gold but don't expect them to understand you 100% in live support