It is possible to take pictures through virtually any telescope with a digital camera, there are however some important things you should bear in mind before choosing one. Most birders already own a scope, if you don't and are thinking of getting one, think first about whether you will want be able to use it for digiscoping before you buy.
The size and quality of the eyepiece is one of the most important factors for digiscoping, it is essential that you try to get one that has a large eyepiece lens, this will help reduce vignetting and transmit more light back into the camera. Most telescope manufacturers now produce long eye relief or wide angle eyepieces and these are the ones to look out for. However advances in technology have meant that some zoom eyepieces are so good that they can produce excellent results even when used on their maximum magnification.

A larger objective lens will help when using a still digital camera, the extra light gathering will increase your shutter speed allowing for pictures to be taken in lower light or faster shutter speeds to be achieved. It is possible to use both angled and straight scopes for digiscoping, most users tend to prefer to use an angled, the combination of the angle of the eyepiece and gravity make it easier to hold a camera to the eyepiece.