Unless you're shooting with studio strobes or using a tripod, you will get better results from the IS lens. Keep in mind if you're shooting digital (or even color film), the sharpness difference between the two lenses is minimal. See
William Castleman's comparison between the two lenses for more details.
Where to buy: B&H and Adorama are probably your safest choice if you plan to order from a New York-based store.