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.
UK#
All wikicreole markup characters are visible on UK keyboards; accessible either by single key press or Shift+ key press.
PL#
The backslash (\), pipe (|), square brackets (), curly braces ({}) and single quotation mark (') require pressing an additional function key on polish(214) keyboard. The morep opular polish(programmers) keyboard layout is practically identical to the US layout.
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.