RegExr - RegExr.com is an online tool to learn, build, and test Regular Expressions.
RegexBuddy - RegexBuddy is your perfect companion for working with regular expressions.
rubular - A ruby based regular expression editor
RegexMagic - Use RegexMagic to generate complete regular expressions to your specifications by using RegexMagic's flexible patterns, instead of the cryptic regex syntax.
RegEx Generator - RegEx Generator is a simple-to-use application that comes with the brilliance of intuitive regex and is also helping you out to test the regex.
RegexPlanet Ruby - RegexPlanet offers a free-to-use Regular Expression Test Page to help you check RegEx in Ruby free-of-cost.