Through my travels through the internets, I have stumbled upon a very useful resource. It is a site (written in rails of course) for testing your regular expressions. It has a very clean interface and uses fancy ajax to give you real time results about your regular expressions. The URL of the this site is http://rubular.com/
Not only does it provide real-time feedback on your regular expressions, it also will give you information about your matches. This is much more useful than trial and error in your code. Also, if you have an error in your regex, rubular will let you know about it.
A little rusty on your regex skills? No problem, the site even includes a box at the bottom detailing all of the most important regex strings. So be sure to check it out
+1
I've been using this for months now and it's been a life saver.