For day-to-day shirts/trousers/suits I use
www.jantzentailor.com (in Central)
Top Range....you cannot beat "A-Man Hing Cheong" in the Mandarin Oriental (not cheap but if you get a classic style you'll have it for ever).
M10, Mezzamine Floor, Mandarin Oriental
5 Connaught Road, Central, Hong Kong
Ph: (852) 2522 3336
If youre just after shirts then Ascot Chang Ph: (852) 2523 3663 and David's Shirts Ph: (852) 2524 2979 are v.good too (both in Central)
Steer clear of the Indian touts around the Star Ferry! Completely ****e & smell like cabbage.