Which lens for portrait shooting on a Canon XT?

I am considering purchasing the Sigma 105mm Macro lens, I've heard it's great for portrait too. I'm wondering if I get that, whether or not it's worth it to buy the Canon 50mm f/1.8 lens, if it will give me a better result or the same.

-Michelle

Longer lenses are traditional for portraits because they have no distortion and offer a lot of depth-of-field control. The 85mm focal length is considered "normal" for portraits and 105mm is good, too. However, the 1.6x digital crop factor on the Canon EOS Digital Rebel XT can make using telephoto lenses difficult for portraits. Sometimes there just isn't enough room. A lot of people like the 50mm lenses for portraits with the 1.6x and 1.5x (Nikon) digital SLRs because you don't have to move too far away to get your subject in the frame. And the large maximum aperture and image quality offered by the 50mm prime lenses makes for very nice portraits.

If you have lots of room to work then the 105mm will be fine, plus you get the macro capability of the Sigma. And that is considered to be an excellent lens, although the auto focus is pretty noisy. I have a 50mm f/1.4 which I use for portraits sometimes. But most of the time I use my Tamron 28-75mm f/2.8 XR Di lens. It's the lens that's on the camera the most, the maximum aperture offers nice shallow depth-of-field at 75mm, and the image quality is excellent.

I have never used an 85mm but would love to try one.
However, I DO have a 50mm f/1.8 MK II lens and I LOVE IT!!! I shoot more portraits than I do anything else.