Angkor Wat
O. K. Some people do come here only to see Angkor Wat. A 1,000 year old temple complex, covering dozens of square kilometers in the jungle. A few (thousand) other web sites can tell you a bit more.
Phnom Penh
The capital city, located in the center of the country. Situated on the Mekong and Tonle Sap rivers, this city of over a million people is growing every day.
The smaller towns
Small towns, small cities, and everything in-between. Some of the bigger towns are Battambang, Koh Kong, & Kampot. And of course, Sihanoukville.
Jungle To the North
and South-East are untouched jungles. Lions and Tigers and Bears. Some can be reached by road, some by small plane, some only by motorcycle, and some cannot be accessed at all. You do need to take precautions when going into the jungle (like appropriate clothing, medicines, food and a map would be nice)
Transportation
Flights into Cambodia generally go to either Phnom Penh or Siem Reap (Angkor Wat) Once you're in the country, the most common forms of travel are by road (bus, taxi, bicycle, oxcart, or motorcycle) and by boat in the rivers or ocean.
Cities
The big cities have a host of rooms from $2 to $2,000 a night. $2 gets you a bed, fan, and light bulb. For about $10 at most places, you can get a nice room with air-con, cable TV, and hot water. Cheap. Phnom Penh, SihanoukVille and Siem Reap offer the finest luxury 5 star hotels to be found.