Regarding types of visa

Hi, I have a question. Me and my friends are going to be visiting  Vietnam with a round trip tickets, but during our duration in Vietnam,we are planning to make a small visit to the neighbouring countries, such a Thai, Cambodia etc. either by plane or by bus and then returning back  to Vietnam again because we are catching our plane to return back to our home country from Vietnam.
 
 So what type of Visa are required of us?