Phmom Penh - is the capital of Cambadio with the histoy of the killing fields. Central market.
Battambang - Bamboo train
Krong kampot national park = very touristy
Sihanoukville has a beautifull beach
Siemreap - where the Angkor temples are
Phom Kulen national park
Mondulkiri - hills and active activities and elephants!
Koh rong sanloem (book ferry 24 hours in advance to and from Koh rong and bring money!)- island in front of the coast of Sihanoukville, it is very pretty.
secret beach named clear water bay.
THere's a jungle route which you can find near Eco sea beach which will take you to clear water bay (30 minutes).
M'pay bay (on Koh rong island)
Swimming with the plankton :O
Angkor Wat ofcourse