Bibliothecae

• BL (character set unknown)
• Univ. of Tront Library (character set unknown)
• BNF (ISO-8859-1)
• Bodleian Library (ISO-8859-1)
• Library of Congress (ISO-8859-1)
• NACSIS Webcat (ISO-2022-JP)
• ICU Library (EUC-JP)
• Keio Univ. Library (EUC-JP)
• NDL (EUC-JP)
• Sophia Univ. Library (Shift-JIS)
• Waseda Univ. Library (Shift-JIS)
• Univ. of Tokyo (X-SJIS)

Librarii

• Bibliofind & Amazon.com (character set unknown)
• Bookfinder.com (character set unknown)
• Maruzen Back in Print Service (character set unknown)

Investigatio

• Yahoo! Japan (character set unknown)
• Yahoo! USA (character set unknown)

Libri latini electrici

• The Latin Library (character set unknown)
• Christian Latin (character set unknown)
• Homepage of Anders Winroth (Gratian's Decretum) (character set unknown)
• Texts from and about the Medieval Period (character set unknown)
• A Hypertext Book of Hours (character set unknown)
• The Labylinth (ISO-8859-1)

Lingua latina

• Latin Dictionary and Grammar Aid (character set unknown)
• Hard Little Words (character set unknown)
• Latin Language (character set unknown)
• Nuntii Latini (ISO-8859-1)
• Latin and Greek (ISO-2022-JP)

Formulae litterarum

• Unicode (UTF-8)

Defining the `charset' is the best way to make your website legible for everyone.
I found UTF-8, the default character code for XML programming, most useful and potential.