To my surprise there are not very many volunteer opportunities in Cambodia.
I did find two very different organizations.
Tabitha-Cambodia -
Offers volunteer opportunities in Cambodia helping the marginalized portions
of the population. Tabitha is the cheaper of the two operations, but provides
less support for the volunteer.
i-to-i
International Projects - Provides a variety of volunteer work experiences
including teaching English as a foreign language, community development, conservation,
construction, and free TEFL training. i-to-i is one of the largest volunteer
service organizations and their service is top quality, but they are expensive.