It is not as cheap as the rest but I like Broadway Cinemathequ store in YMT. I can find many panasian dvds for better than net prices. You have to be member to get better prices (the first time I was there I thought they were discounted prices so I bought more than I intended and at the cashiers I suffered a shock, but the guy was too kind and allowed me membership prices - using another member's card) but if you know someone in Kowloon who loves cinema, they are probably a member anyway and you can use their card (members get credit if they buy a decent amount and have perks like free film tickes in their cinemas).

I also like to shop there because it is not as crowded as Original and the other shops in Mongkok (also if you buy more than ten then you can bargain and will probably get a discount- I get one each time :) )

A good place for original Korean dvds is at a tiny underground mall in Mongkok (I can't find the place but don't know how to describe it-Kozo knows it though and maybe he can give a better address)

The people there are very hepful but again bargain, they give you discount even if it is just two dvds. Also these shops usually open after 13:00 so don't go there early in the morning (there are two good ones, one in the entrance and one at the very end -both to your left as you enter the tiny mall).