Check out the Two Dragons Guesthouse-run by an expat. I kept getting ripped off in Siem Reap til I went there. He has good drivers. They also have a good, reasonably priced restaurant as well. In the rooms, they have an immensely helpful how-not-to-get-ripped off/things to do tip booklet.

Honestly, his rooms are cheap enough you'd probably make out better by renting one of his rooms, using him to get tours, and-if you don't want to stay at that cheap place (which is not high-end by any means)-staying somewhere else.