Hong Kong will blow your mind. There are few places in the world like it. By far the best (and cheapest) way to see Hong Kong Island is by riding one of the many double-decker trams.
For as little as HK$2.30, you can surf your way through a man-made cavern of lights, uber-modern skyscrapers, street hawkers, oriental smells, and of course tons and tons of people.
Even better, try hopping one of the many trams at night. That's when the city that never sleeps really comes to life.