I'm going traveling to Thailand, Laos, Cambodia and Vietnam. What's the best way to get around there?

The land crossing from Bangkok to Siem Reap used to be quite difficult, but now it is easy. From Siem Reap you can head by boat to Phnom Penh and make a stop there head to Saigon by bus. Vientiane is not really interesting, the best place in Laos is Luang Prabang. You can fly from Saigon to Vientiane and then head on to Luang Prabang by bus..