In Phnom Penh, I would be sure to visit Psar toul tom poung (Russian Market) It’s a great place to go shopping. As far as foods, I don’t know how extensive you travel and what your palate is like but they have banh xeo which is a cambodian omelet. Very tasty and cheap
Soriya mall is awesome - it’s a sign of western influence and has some good food court action (you need to buy vouchers there to pay for food)
There are a few good casinos in the Phnom Penh too. There is one I can’t recall that has a good band and free all you can eat food if you’re a patron. Just dress decent and it’s a good fun time for late at night
clubs: U2 and Spark, ask anyone and they’ll know of the club
KFC - it tastes different
Silver Palace/Royal Palace - very beautiful be vary quiet and respectful here and make sure to remove shoes when inside the pagodas.
Tuol Sleng - http://www.tuolsleng.com/ - old french school site of political prison - very very shocking
The killing fields are out side of phnom penh but you can visit them.
http://www.killingfieldsmuseum.com/genocide/genocide.html
If head along the river bank at night, there are a bunch of great restaurants that have live music and some dancing. it’s great nightlift, but US prices
If you have time, make it out to Sihanoukville aka Kompong Som, it’s the beachside in cambodia to the west
In Siem Reap, be sure to go to Banteay Srei. It’s one of the temples in the Angkor complex and one of the best. The history and architecture is amazing.
Also be sure to visit Phnom Khulen it’s about 30 minutes outside of Siem Reap and is known as the King’s playground, home of the 1000 lingas. It’s about 20 bucks for foreigners to get in and you need to go during certain hours since you can only go one way up the mountain but REALLY WORTH it.
The best restaurant in Siem Reap is here
Siem Reap Nº. 117, National Road No 6, Sala Kanseng Village, Svay Dangkum Commune, Siem Reap District
I think at 7 they start their buffet (really good), something around 14 bucks and they have live dancing by a childrens troupe. It’s all classical cambodia performances. Be early because the Korean tour groups overrun the place so make sure to arrive early for food. In the morning, their Kutieu (noodle soup) is amazing. Great breakfast spot
You can also check out the Cambodian Cultural Village down the street.
http://www.cambodianculturalvillage.com/
The National Museum is okay but expensive for tourist. I would be sure to ride a tuk tuk around siem reap at night. it’s beautiful
http://www.phnomenon.com/index.php/cambodian-food/phnom-penh/russian-market/
That’s all I can think of for now, I’ll try to come up with more ideas as they come.
Have fun and good luck!