Helistar Cambodia (http://www.helistarcambod...), a VIP helicopter charter and scenic flights company, operate to virtually anywhere in Cambodia. Helicopters can be chartered to fly from Phnom Penh and Siem Reap for one-way or return journeys. The basic hourly charter rate is US$1700 per flight hour plus 10% VAT and 10% SPT. They operate modern, air-conditioned French-built Eurocopter Ecureuils with luxury leather seating for up to 6 passengers. They also have licenced Australian and foreign pilots. A pick-up and set-down transfer service is also available at both international airports.
Ferries operate seasonally along many of the major rivers. Major routes include Phnom Penh to Siem Reap and Siem Reap to Battambang. The Sihanoukville to Koh Kong ferry no longer runs. Boats are slower than road transport, charge higher prices for foreigners, and are sometimes overcrowded and unsafe. Then again, Cambodia's highways are also dangerous, and boats are probably the safer of the two options. The high speed boat from Phnom Penh to Siem Reap costs US$33 and takes about 6 hours, departing at 7.30am, and offers a spectacular view of rural life along the Tonle Sap river.
There is also a few luxury boats operating between Siem Reap, Phnom Penh and Saigon. For something around 150$/day including accommodation, food and excursions, it's a good alternative to regular boat service.
The boat trip between Siem Reap and Battambang takes longer especially in the dry season, and is less comfortable and more expensive than taking a seat in a share taxi, but is favoured by some travellers for its up-close view of subsistence farming and hundreds of waving children along the river. Taking the boat late in the dry season April and May is not advisable as low water levels mean that you must transfer to smaller vessels in mid-river.