Travelers in Vietnam can tour the entire country by bus, from Hanoi to Ho Chi Minh City for less than $40 (as of October 2010). Buying an open bus ticket from any travel agent in the country will allow you to hop on and off of 24-hour (sleeper) buses throughout the country. Tickets have fixed validity (from four days to three months), depending on where you purchase them.
Phnom Penh and Siem Reap are both accessible by long-distance buses from Thailand and Vietnam. Visit a travel agent in Ho Chi Minh City or Bangkok to arrange travel, or ask at your hotel if you're already in Cambodia for onward travel by bus. You can buy tickets nearly anywhere. Expect to pay about $20 from Siem Reap to Bangkok and less to get from Saigon to Phnom Penh (as of January 2010). Beware, traffic is slow and buses don't all have bathrooms.
Getting from Bangkok to just about anywhere is cheap and easy with Thailand's extensive bus system. Tour the country at your own pace. Tickets are available from most travel agents, who can be found anywhere in Bangkok's Khoa San Road area, or from bus terminals directly. Buses are always air conditioned.
