Was on the IMTRAV Majestic Angkor trip back in November (3-9), and wanted to recommend a fun side trip that we took on our "day off" there in Siem Reap.
We hired the motorcycle taxi driver that I used to get in from the airport, Thy Srey, and a couple of his friends to take us down to the flooded forest of Kampong Phloc...absolutely amazing trip, and it is definitely worth checking out.
In fact, we enjoyed our time with Thy so much that I built him a website to try to send more business his way. Please check it out if you're so inclined. He's trying to get into the tourist business in the Angkor Wat area, but it's a tough thing to break into due to an "old boy's" network of sorts. He's a safe, punctual, and reliable driver, with reasonable rates for a daily trip.
If you'd like more info, or have any questions, I'd be happy to help...email me at firstname.lastname@example.org
Enjoy the trip, whatever you choose to do!