I have the 50mm 1.8 for my Canon 20D, but don't use it very much. When you are in a typical small studio situation, you often still can't get back far enough even with a 50mm (80mm crop factor), especially for full length shots. So what I normally use in the studio is the Sigma 18-125 for medium to full shots and the Sigma 70-200 2.8 for medium to head shots. The Sigma 18-125 is moderately sharp which is just right for glamour which you usually need to soften a bit anyway. Since you'll usually be at f8 and f11 in a studio, you're at the sweet spot of the lens. The 70-200 is ultra sharp (full equal to the Canon L lens in reviews). This is a bit too sharp for glamour so you always have to do some post processing to get rid of the ultra sharp skin which shows every pore, etc.
Wow, that's sharp, was Emilia's response when shot with the Sigma 70-200 2.8.