Nav Canada and FAA are the only legal for aviation weather sources, but the more you know about the weather, the safer you will fly.
Nav Canada Forecasts and Observations
Nav Canada's Forecasts and Observations Page - Weather and Flight Planning
King City Weather Radar
Environment Canada King City weather radar (slightly different scale than Nav Canada's)
ADDS US Weather
NOAA's National Weather Service
Aviation Weather Center
Aviation Digital Data Service (ADDS)
This is the official US aviation weather source. The Java tools are especially useful.
Davis weather reporting stations owned by independent operators.
Weather station at Edenvale Aerodrome - not legal for flight planning, but useful nevertheless.
Nav Canada - Local Area Weather Manuals
Local Area Weather Manuals are produced for each region of Canada and describe typical weather patterns by season.
Weather Network, link to Port Perry.