A good guide to shopping in Toronto is published by Toronto Life magazine. I bought the 2005 Shopping Guide this year for the first time. You can find all kinds of shops to suit everyones style. For fashionistas, this guide is a must. It has a lot of entries and the catagories cover: fashion, beauty, home, garden, books and music. The guide should be available at your local magazine seller or online. There is an online version of the shopping guide, I am unsure of how much it differs from the print version. It is included in the City Guides section of the site. There is tons of great information that includes food, restaurants, fitness, kids, entertainment and getaways.
I also just noticed a great little monthly shopping column on the site called The City's best loot.