The most comprehensive weather provider in the world. Worldwide converage with no fees or subscritions.
A free service providing Canadian and Atlantic weather data. International flights orginating in Canada require a subscription based provider (Jeppesen) or the use of the the FAA's weather service. Some links to the US system are provided.
Similar to the FAA but a bit difficult to navigate.
Offers a barebones free service to UK pilots flying within the UK. All other services are offered an a subcrition basis.
Math and Physics for Pilots
Boeing 737 - 800 Flight Planning and Performance Manual