One moth travelling: Thailand for a week but where else? Cambodia, Laos or Vietnam?

I definitely recommend Cambodia and Vietnam, these two countries are really easy to combine. I recently returned from a trip through Thailand, Cambodia and Vietnam and my highlight was visiting the Angkor Temple Complex in Siem Reap but also travelling through the Mekong Delta into Saigon from Phnom Penh. I travelled independently and booked my trip through: http://www.cambodiaonline.com.au