I used Synon's services last year, thanks to all the great feedback from you guys! He was very friendly, proactive and always had ice cold towels and water to hand

I wrote a review on my blog, where I talk about costs, as well as posting up my full itinerary with photos: Touring the Temples of Siem Reap

I would particularly recommend heading out to Koh Ker for a day. It is a long drive but the temples are absolutely worth it and at $100 I think Synon's price was very fair indeed.