The Mad Monkey hostel was founded by, and is still run by, British and American travelers. Although the location is not central (it is in a prime area near the embassies), it is my favourite hostel in Phnom Penh. The staff are always very friendly (especially Tina, who in my opinion is the happiest person in the world), the rooms are spacious and very clean, and the hostel has a good area for socialising. The bar and restaurant are a real highlight; despite the prices being a bit expensive for Cambodia, the food is delicious. I've stayed in both a shared room and a private room, and the experience was fantastic each time.