Siem Reap is an excellent place to buy Cambodian souvenirs, handicrafts, textiles and art. Only Phnom Penh offers a comparable selection, but much of what is available in Siem Reap is unique to Siem Reap. Until recently, the Old Market (Phsar Chas) and vendors at the temples were the only places to buy souvenirs. Over the last few of years there has been a small boom of new shops, galleries and boutiques, offering a more varied selection of quality handicrafts and silks as well as original artistic creations - paintings, prints, carvings and such.
The Old Market still has the widest variety of souvenirs, as well as the best selection of items such as baskets, silver work and musical instruments. It also offers an interesting local ambiance, but the boutiques, galleries and specialty shops offer generally higher quality items and a more sophisticated selection of Cambodian products. Of particular interest are the traditional craft workshops and silk farms where you can see crafts in the making as well as buy the final product.
When purchasing local crafts, be selective in your purchase as there might also be some fakes. Most of the crafts, particularly the carvings, silk products and silverwork are hand-made, making each piece a unique work. Masters as well as students produce much of what is available, so some pieces are significantly better than others.