Everything is being sold here. Antiques, T-shirts, jewelry, pirated copies of books, arts and crafts, food, snacks - you name it, it's probably there. Walk through a wooden maze of stalls to hunt for the things you think you want or they think you should need (grin)
What to pay: Bargain.
I do not want to be condoning piracy but I do know these are very popular with backpackers. For US$5-US$10, you can bargain hard for pirated coloured copies of "Lonely Planet" guides - usually of Cambodia and the neighbouring countries like Thailand, Laos, Vietnam, Malaysia & Singapore. The quality ain't bad - and you save a lot of money compared to the originals but I leave it to you as reader of this tip to make a judgement call for yourself with regard to respecting copyrights.
What to buy: "Lonely Planet" guides.
What to pay: US$5-US$10. Bargain HARD.
The Old Market (Psar Char) is a great place to go souvenir hunting. While the market is a bit run down, there's a good choice of items and prices are OK - definitely much, much better than the large souvenir shops on the edge of town. It's fully open during the day, and some (but not all) stalls stay open for the early evening too.
Don't be afraid to bargain, but remember the stallholder's livelyhood too!
What to buy: Pretty much all the souvenirs you'll see elsewhere are available here.
What to pay: I got a nice selection of gifts for 10 US dollars...
What to buy: In many souvenir shops you will find reproductions of some of the carvings that you can find at the Angkor temples walls. They are made of clay and painted to look old, you can find them in any size and weight.
The Lazy Mango is a great little second-hand bookshop. If you need something to read on your travels, it would be worth stopping by here to check it out. Not the cheapest of places, but the books were in pretty good condition, and you should be able to trade your old ones in there, too.
They have nice postcards, too!