Siem Reap: the town's name means "the defeat of the Siamese." It is a quite little town today, nestled along the banks of the Siem Reap River.
The Singapore Raffles Group has renovated the Grand Hotel d'Angkor. Bigwigs from Jackie Kennedy Onassis to Charlie Chaplin have stayed in it. King Sihanouk has a small villa across from the hotel, but he rarely uses it. Foreigners can usually get a tour of the grounds, though not the insides...
The city's Old French Quarter is by far the most charming place in town. You could be in Tunis. Lots of cafes and guesthouses. And the New Market, just south of the French Quarter, is the best place in town to buy odds and ends to remember the place by.
Just because the town is laid back doesn't mean it isn't prepared for you. Enough tourists come through Siam Reap so that a variety of levels of accommodations are now available and the town has plenty of pubs and restaurants. There's even a mild nightlife (including at least one disco) and an Internet cafe' (where at last report the going rate was a buck an email). Shops and stalls also exist along the Airport Road and along Route 6 east of the river.
For a good overview of places to stay in Siem Reap you can look at the page that Tales of Asia has online.
Check out the Angkor Conservatory just outside town. It sells replicas of Angkor Wat, along with other local arts and crafts.
Just taking a walk along the river or through some of the smaller back alleys can be educational. You get a glimpse into everyday Khmer life. If you want a deeper glimpse into Khmer life, inquire about day trips onto Cambodia's huge lake, Tonle' Sap. Among the thinks to see are the floating villages that exist on the lake. Look for a boat with a good roof or you will be baked like a lobster when you return...
Most people come to Siem Reap to see the ruins of Angkor. The town itself is just lucky enough to be there.