Wikipedia:Keyboard_layout
has images of keyboard layouts from different countries.
http://www.microsoft.com/globaldev/reference/keyboards.mspx can display different keayboard layouts.
Also see OLPC keyboards.
US#
All special markup is easily available.
UK#
All proposed 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 more popular 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.
FR-fr (AZERTY)#
All proposed markups are available. Most markups need an additional key (AltGr+key). Some of them (the potential ^ and ~) must be pressed twice since they are considered as modifiers for other letters.
FR-ca, EN-ca (Canadian multilingual)#
The Canadian French keyboard comes in several flavors. Nevertheless, all proposed markups are available. Some markups need an additional key (Shift+key or AltGr+key). Some of them (depending on the chosen layout) must be pressed twice since they are considered as modifiers for other letters. There is a problem however from French Canadians purchasing US-English keyboards (most of them are outside of the province of Quebec). If they change their layout for a French Canadian one, important markups (like square brackets ([]), greater/lesser-than (<>), slash (/), curly braces ({})) are not at their respective places anymore. These people must switch back and forth between two layouts.