Here are some great travel companies that we highly recommend.
Ethos - Sapa
Ethos is based out of Sapa, Vietnam. When you travel with them our are helping a true social enterprise that really cares about the local environment and community.
To really see Mongolia you will need to hire a tour company. We loved our tour with New Milestone as they gave us an amazing local experience so it did not feel like a tour.
No better way to see Cambodia than the way a local would it by motorbike. Green Frog Adventure tours offers a host of really great motorcycle adventure tours.