On the page I mentioned there's a rather big list of characters that you can produce with the AltGr key in MS Word (doesn't work in my Notepad) on the US keyboard.
AltGr+R for example is the registered trademark symbol, AltGR+7 is a half (can't see the logic, but it's shorter than alt+1+7+1) and AltGr+? is the Spanish inverted question mark. On the Dutch keyboard, to name another example, we've got AltGr+- for the backslash (and that's why I started to hate the Dutch keyboard in the good old DOS days).
Isn't it amazing that even a keyboard has its secrets? Be frank: how often do use the keys right to the Alt Gr key. That's the key with the Windows symbol on it (Win E starts Explorer, Win M minimizes all windows) and the context menu key (same as right mouse click). And then there's the mysterious scroll lock.