Internationalization (I18N) Resources

iso 8859 alphabet soup is a pretty good explanation of various single bit character sets, though the Wikipedia page for ISO 8859 is now better.
Likewise, the Wikipedia page for Unicode is fairly good, thought the official story is at the Unicode Consortium
Multiple languages in html is a good example of pages done in multiple encodings
The i18n activity at W3 is a good resource, especially the deck for Weaving the Multilingual Web
W3 also as a good collection of Internationalization notes in their Web Design and Applications section
IANA maintains a list of canonical character sets
LEO has a good English / German dictionary for those of us who have forgotten our high school German
Google translate is useful in a pinch
The UN universal declaration of human rights is a useful source of test data, as there are translations in every language imaginable, along with PDF versions with embedded fonts. Often cutting and pasting from these turns out to be a great way to test systems for transcoding issues.
While a bit old, Programming for the World is a great overview of i18n issues and techniques.

Internationalization (I81N) Resources