Cambodia is one of the country that gives Visa Free for the ASEAN (Association of Southeast Asian Nation) members. Since it is one of the middle country aside from Laos to travel from Thailand to Vietnam or vice versa, I consider travelling to Cambodia after next month to Vietnam.
Listed below are the visa duration for some countries, including ASEAN members:
There are several exemptions and policies posted below, but for some information I might not have include in this post, please refer to the Official Cambodian Immigration Site.
I hope this post helps you to find out about the duration of visa your passport is entitled to.