[Wikipedia:Keyboard_layout] has images of keyboard layouts from different countries.

[http://www.microsoft.com/globaldev/reference/keyboards.mspx] can display different keayboard layouts.

!US

All special markup is easily available.

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!UK

All proposed wikicreole markup characters are visible on UK keyboards; accessible either by single key press or Shift+ key press.

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!PL

The backslash (\), pipe (|), square brackets ([]), curly braces ({}) and single quotation mark (') require pressing an additional function key on polish(214) keyboard. The more popular polish (programmers) keyboard layout is practically identical to the US layout.

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!DE

Nearly all markup needs an additional key, either Shift+key or AltGr+key. But at least all the symbols are visible on the keyboard. 


Also see [OLPC keyboards].