book 15-25 May, travel by 30 September. Cheap tickets from BKK to SR for once.
http://www.cambodiaangkorair.com/en/

Air Asia fly from Don Muang airport to Siem Reap twice a day. So compare the prices before booking.

Looks like AirAsia just announced a sale to compete directly with this one (at about half the cost on the airfare) but once you factor in AirAsia's luggage fees and add-ons it ends up being the same/a bit more.

Cambodian Air has the added benefit (at least IMO) of being able to fly out of BKK and not DMK.

Flying out of BKK is a big positive to me, but the last time I flew Cambodian Air, their higher baggage fees brought the fare up to about the same as BKK Airways. This sale is a significant decrease though. I may book a seat now "just in case".

I do hope this motivates Bangkok Airways to lower their prices, as I do like their service and schedules.

Particularly handy for flying to/from PP into SR; at $35 one way, significantly better than traveling overland, especially now with the road all torn up and rain coming.