For fish oil, I've been taking Equazen mumomega, which is sold at my OB's clinic (Central Health). However, I've also noticed that they're available at Bumps2Babes and Mannings (look in the pharmacy section of the IFC branch). It has no smell or aftertaste whatsoever and you take one capsule a day. I can't remember how much I paid, but I think it was around HK$180 for 30 capsules.
As for prenatal vitamins, I'm taking Pregnacare original by Vitabiotics. This is available from Mannings (look in the pharmacy section) and Bumps2Babes. It costs around HK$79 for a 30-day supply.