Cambodia currency

I tried to post this yesterday but somehow it missed.

I'm going to Cambodia in a couple of months. I am confused about the currency used. What is its value compared to US$ Thai Bt or UK┬г. I cannot find this information anywhere. I tried Aol money conversion but it doesn't cover Cambodia. I would like to be able to work out how much I'm being charged. If I don't know the value it is too easy to be overcharged.
I believe it is sometimes required to pay (or is possible) in US$. What is the best denomination to take, 10. 20 or 50?
Many thanks.

http://www.oanda.com/converter/travel

Many thanks Boygeenyus, just what I was looking for.
Can anyone help re the US$ issue?

[gearguy]

take 1, 5, maybe some 10, few 20. no 50 or 100; you will find it hard to use and hard to get someone to break them as well. Lots of couterfeit 50 and 100 in asia, so many won;t take. Take good looking bills but not new if you avoid it and also no bills which are old, torn, written on, etc. Some vendors are particular. I've had them refuse and ask for different bills, or ask for smaller bills.

The value of smaller bills, is that many places, will give you change in cambodia, which will be pretty worthless.
Have lots of 1s when ypu visit ankor to give the kids who will come up to you and want to help you, practice their english, etc. It's a buck and will really help out. When I was at ankor, there was this one kid, real cute, may 12, spoke really pretty good english and introduced us to a fortune teller. It was a fun experience; cost me all of a few bucks.

The fortune teller told me I would soon have a lot of money, million or more. So I then left and went to vietnam, hit and ATM and asked for $100 USD, got 1.6 million dong. So he was right, I had a lot of money, just it was not USD.