Hmm.. capital city of Cambodia with some development going on. For my opinion, its standard of living will be better than Siem Reap. A suggestion to visit both Siem Reap and Phnom Penh and you will get the different feel of them. It's a nice experience though as we took an air-con Express Bus from Siem Reap to Phnom Penh within 5-6 hours due to the condition of the bumpy road along the journey with a short break. The bus fare ranges from USD6 to USD 10.
Nothing much to shout about in Phnom Penh except for the Tuol Sleng Genocide Musuem/Killing Field (the cruel Pol Pot), some western restaurants at Riverfront (lot of choices for your selection), Royal Palace & National Museum (good recommendation by many).I think photos are better than my words here :)
> Post Office - A postcard back to Kuantan for my mum.. ^_^
> Wat Phnom (USD1)
Have no idea what was it about.. Getting confused after reading it.. 
> Sorya Market (items in USD, but can pay in riel)
> With the Owner of the Inn
> Guess it must be something to do with Internet company (service provider?)
> National Bank 
> Tuol Sleng Genocide Museum (USD2-3)
> Actually Tuol Sleng was a high school.. 
> Killing Field (USD2-3)
> National Museum (USD3)
> National Monument
> Tuol Sleng Genocide Museum (USD2-3)> Actually Tuol Sleng was a high school.. > Killing Field (USD2-3)> National Museum (USD3)> National Monument> Royal Palace
> Famous RiverFront Area
> Friendship Between Cambodia & Vietnam
> Famous RiverFront Area> Friendship Between Cambodia & Vietnam> Final Lunch before leaving 
> Phnom Penh International Airport
> Phnom Penh International Airport 
> Departure Tax (USD25 for non-Cambodian)
Overall, I enjoyed my Cambodia trip as i had the opportunity to learn their cultures and visit their Heritage Sites.. Wonderful! :P
Some souvenirs to bring back home...
