useful for testing regexp http://myfluffydog.com/programming/php/scripts/regexp.php
Oreilley Article on Regexp http://www.onlamp.com/pub/a/onlamp/2003/08/21/regexp.html
regexp for eudora http://www.cecilw.com/eudora/regexp.htm
Wikopedia has a nice article http://en2.wikipedia.org/wiki/Regular_expressions
Complicated looking tutorail http://gnosis.cx/publish/programming/regular_expressions.html
"Official" Perl tutorial http://www.perldoc.com/perl5.6.1/pod/perlretut.html
Good looking explaination http://www.mozilla.org/bugs/text-searching.html#regex%20basics
Port of the KDE Regexp editor to Windows http://www.cfregex.com/
Expensive windows editor, Powergrep http://www.powergrep.com/
RSS .91 spec http://my.netscape.com/publish/formats/rss-spec-0.91.html#example1