Taxis are abundant in Hong Kong. In most city areas, you'll find just the regular, red taxis; in the mainland New Territories there are green taxis, while blue taxis serve most of Lantau Island.
Red taxis are priciest; flag falls and per distance rates for the green and blue taxis are lower, as they tend to cover longer distances. There may be extra charges, for bags, tunnel fees, phoning for taxis.
In the main downtown areas, you can flag down taxis in many places - but not where there's a fence alongside the road. Scattered near the harbour, there are ranks for cross-harbour taxis: Hong Kong Island taxis that have wound up on Kowloon side, and vice versa: take one of these, and you only have to pay a one-way tunnel fee, as the driver returns to his (most drivers are guys) area.