Hi there,
Been recently to Hong Kong for a "small" city trip.
I can recommend most things already said here,
Personally I liked Cheung Chau island a lot aswell, nice to go for 1 day, you can walk around the complete Island easily (or bike), no cars allowed over there.
Great & extremely cheap (sea)food
@ Tai-o, you can take a boat trip to see pink dolphins, but unfortunately for us we did not see them...
Shek-O & Big-Wave beach are also really nice. And worth the trip. If you like walking, there is a trail that starts @ Big-Wave beach, taking you over the hills with a fantastic view!
@ Stanley, go eat chez le suisse... (don't recall the real name of the restaurant) but ask for him, most people living there will know. Great food for a great price (a lot more expensive during the weekend)
Going to stanley, try to take bus 2X if i remember well, and try to sit top level, front seats, a ride you will not forget.
If you miss the belgian cuisine, "Frites" is a good restaurant with all the goodies (beer) from here

(More or less in Soho, but I think there are a couple Frites restaurants, correct me if I'm wrong)
If you are into computers, try visiting the Golden Arcade, the most impressive computer market!
(try not to take the wife/girlfriend with you

) (Kowloon)
The peak is also quite nice when it is dark, with a good sushi resto there. (bit expensive though)
If you take the good things, easily 100 à 150€ a person.
Peninsula bar as suggested. (Also a good rooftop bar in New York by the way, with Duvel @ 15$

)
Grand Hyatt hotel is really good, at the Expo, although, if you want to travel alot with the subway, it's a bit far from the station. As long as the new line is not finished. But taxi is really cheap.
Hong kong park is nice , with the bird section. (free)
If you want to go up in the IFC building , take legitimation with you. Free of charge.
On the other side of the water, the DHL balloon might be nice, as you have children with you...
Also try to do the elevators in Soho.
If something pops up in my mind, I'll post it here.
We flew Qatar (as usual

) Which was a very good experience. (and close to being the cheapest, plus start from Brussels with avoidance of all the major airports in Europe! ) Plus is/was the flight back from HKG @ 01.00 AM local time, which gives you a full last day.
Sorry for spelling mistakes/things I forgot, but had to type this in a hurry.
Grtz!