After learning about the US Census's TIGERLines datasets I've working with the following layers, from the USA data

• Country boundaries
• State boundaries
• County boundaries
• City boundaries
• ZipCode boundaries

What I'm trying to find is the equivalent (where appropriate) of the same data for the following countries.

• United Kingdom (hello Ordinance Survey :( )
• New Zealand
• Canada
• Italy

... but i'm struggling to find any data available.

Can anyone help me?