Hong Kong is unusual in that most of the major banks sell gold coins at a very small mark up - spot plus around 50HKD (divide this by 7.78 for U.S.). They also buy gold coins.
Hang Seng Bank (owned by HSBC) for example sells Krugerands, Eagles, Maples, Kangaroos and Sovereigns.
Bank Of China sells Maples, Eagles and Panda's.
Kitco (Hong Kong) sells a wide variety of gold and silver but their range has become very limited over the last 6 months. They do sell Perth Mint products cheaper than Australians can buy them from the site as they don't have to charge GST (goods and services tax).
As Joeka mentioned, just like Singapore, local residents can also have bank accounts denominated in gold - the units used are Chinese though (taels and maces).
There are also lots and lots of gold shops around - local people buy 999 gold jewellery for many occasions and like Indians use it as a store of wealth against hard times. This is sold by spot price plus a small fee for making up. These shops also buy it back.
Although a number of you have mentioned Fake Coins from China if you buy through the banks I don't think there is any problem.
If anyone is on a trip O.S. to Asia you may want to spend a little time doing some shopping for stuff other than the usual crappy tourist souvenirs.