For Windows users, here is another variation on the first method detailed by CoDEmanX. Use the first three steps of his first method, but instead of opening Notepad, in the search bar of the Start menu, type "character map", which will point to the character map utility included with Windows. Open the character map, in which you can select the character(s) you want to use in Blender, and from the "Characters to copy" bar in Character map utility, copy the characters into the Text property field as CoDEmanX described.
A preliminary test suggests that this might also be a way to get an extended ascii symbol into other text items, like object names, although it's not clear that this might not run afoul of other error checking.
Finally, I expect that MACos and Linux have similar character map facilities that can be used similarly to that in Windows, but I have no specific knowledge of those platforms.