Depends on your purpose of visit. But I'll list some must visit place of interest:
Club/Pub: Lan Kwai Fong. The entire Lan kwai fong street are filled with pubs with many local hongkees and foreigners. I have seen many americans there before. So try to make some friends there, they might show you around.
Disneyland: The new HK disneyland
Ocean Park: HK most famous place of interest. A must visit.
Gambling: you need to take a ferry to Macau. There isnt any casinos in HK itself. Only horse racing.
Last but Never Least.. SEX! there are 2 places.. the high and low class whoring area. Temple Street is a place where everybody can afford to stick it in. If you really wanna get steamy with really beautiful chinese chicks, visit: Kowloon tong. That place is paradise.. Most of the motel have chinese gangster or pimps lurking around so becareful, goto a hotel.
I would suggest you to visit HK with a chinese friend or you will find it extremely difficult to visit from place to place.. almost everybody speak cantonese or chinese only.