An excellent introduction to character sets and encodings is in the first chapter of Java Internationalization, written by Andy Deitsch and David Czarnecki and published by O'Reilly. Not only is it fun to learn about the different ways in which people write, but it helps you appreciate the difficulties the Unicode consortium had to overcome when creating this character set.
The Yudit editor and many interesting links to Unicode-related topics are at www.yudit.org.
The GNU recode program, which allows you to move documents among character sets and encodings, is at www.gnu.org/directory/recode.html. Recode is an essential part of my toolkit when I work on Unicode-related sites.