Now the convenient way:
http://allchars.zwolnet.com
AllChars is a freeware resident character composition utility that uses the above codes from a more intuitive interface. You can also see what characters are available in different fonts, and it includes a function to make the NumPad DEL key produce the radix character for your regional settings in NumLock mode.
I find that easier than trying to keep a printout of upper-ASCII codes around while I type or fighting with Windows Character Mapper.
Example: letter Æ is Control, A, E and letter æ is Control, a, e (used in Norse). The cent sign is Control, c, / to yield ¢.
All 256 characters in the ASCII table are available through ALT-numpad decimal codes. This can be a lifesaver if a key decides to take a powder in mid project...
Also, sometimes Gaia fonts get temperamental about international characters! Stupid little #$*^ boxes...