I have a Canon Rebel XTI and would love to go into these areas of photography. Thanks!

All Answers To Questions

If you're going with natural light only, then aperture size becomes important. Canon has a sharp 50mm 1.8 which is good for portraiture. For a more versatile (but more expensive) lens, you can try the 70-200mm 2.8L.

Typical portrait lenses for a film camera start at 85mm and go to 105mm. With the crop factor of 1.6 on your camera you are looking at 53mm to about 67mm. They don't make a lens in either of these exact sizes. Your best choice would be a 50mm F1.4 or 1.8. The F1.8 is a really good lens and is cheap ($100). If you have a zoom lens like the 28-135 or 70-300 you can use that for the higher end of the portrait range.

For indoor shots, make sure your lens has a low aperture. By low i mean lower than f/3 (I know f/3 is not a normal aperture setting but I'm just saying go lower than f/3) For outdoor, make sure it's not a wide-angle lens. A standard or medium telephoto lens would work for outdoor the best. This woud mean around 50-100mm.