Aeronautical Charts (USA, Canada and OZ)

[Dupre]

Does anyone know where I can download VFR charts from the net, or get hold of some old ones for the USA, Canada and Australia?

I'm starting to think about a flying holiday in one of said countries and want to get some idea of what the airspace is like to do some initial planning (doesn't need to be up to date - it might be some time before I go!)

Thanks,

Dupre.