The Ontario Weather Page

Weather forecasts, watches/warnings, radar and satellite images, real time lightning display and road conditions, among other resources.
http://www.ontarioweather.com

Weather for Ontario

Weather forecasts and reports for selected Ontario communities.
http://aweather.torontonian.com

Environment Canada Ontario Weather

Long and short-term weather forecasts for Ontario, includes synopsis, Convective (Severe) Weather Warnings, current forecasts and regional reports.
http://weather.ec.gc.ca/forecast/textforecast_e.html#ON