I've just been through this... today is my last day in Hong Kong having spent 2 weeks here (only weekends shooting though). So far my best pics have been:
* The peak - night shots of Hong Kong city. Get there before sunset (I was setup around 5pm). Don't take from the peak lookout, the view is average. Exit the tower and take the walk to the right (Lugard Road). Walk along there for about 20 minutes and you will get a great view. Best time to shoot is about 20 minutes after sunset... when all the lights are on and there's just a touch of colour in the sky (not black). I took the tram to the Peak and it does get pretty crowded. Tripod is essential and wear a jacket - it can get cold up there.
* There's also a decent view of the city from kowloon side, though this is no where near as spectacular as the peak.
* The gold fish markets are pretty cool, though make sure you ask before taking pics in the shops. Some of them don't allow photography in there.
* Walking the streets - shooting neon. I got a few decent neon shots.
* Lantau island - the big buddha is pretty cool. Sadly though I think the only time to get a decent shot would be late afternoon. The rest of the time the buddha is back lit so all the pics will have washed out background (if you have a look at any of the pics for sale of the buddha, they have all been touched up in some way-the buddha is bronze as well, not gold as it is in most pics). Also worth visiting is Tai O - the fishing village. Loads of character there. I was there late afternoon and got some pretty stunning shots of the sunset.
At the moment Hong Kong is very smoggy, so backgrounds are very average (for landscapes).