A useful flex regex tool

here's some more

http://www.fileformat.info/tool/regex.htm

http://www.rexv.org/

http://www.txt2re.com/ (this one's particularly good for your next acid session)

http://brosinski.com/regex/ for eclipse

http://www.weitz.de/regex-coach/

http://regex.larsolavtorvik.com/

http://www.regexbuddy.com/

(this one costs a few $)

http://www.regextester.com/

(... and the one in activestate Komodo. i don't use any o these, i have my Friedl book and i try to understand the edge and cornder cases, build a test suite)