Electronics is a major one, especially considering the initial high prices. If you're looking to build a beast of a PC, buying all of the components yourself and putting it together is always the best way to go. If you can put together Lego, you can build a PC. That said, taking the time to buy all of your components (RAM, hard drive, CPU, motherboard, etc.) in HK and you can save even more money than buying a pre-built computer, sometimes more than USD 300. Let's take for example the best bang-for-buck video editing CPU, the i7 3770k.
The other major electronics products that are significantly cheaper in HK are Apple products. Instead of simple marking up the price of the 13" Macbook Pro by 10%, they decided to raise it to the ever-auspicious price tag of RMB 8,000, a thinly-veiled attempt to attract even more illogical purchases than usual.