Boeng Kak is the backpacker ghetto for Phnom Penh. Most of the guest houses are wooden and built on stilts over the lake. The guest houses have wooden decking overlooking the lake where you can idle away the time in a hammock and watch the sun set.
It is a cheap area to stay and has all the travel and tour information you need. Like many ideal backpacker spots, there could be a time when the whole area is bulldozed and a new luxury hotel is put up.