regular expressions 101 - Extensive regex tester and debugger with highlighting for PHP, PCRE, Python and JavaScript.
RegexBuddy - RegexBuddy is your perfect companion for working with regular expressions.
.NET Regular Expression Designer - Learn, develop and test Regular Expressions for the .NET platform.
Expressions - An app to play with regular expressions. Easily and nicely.
RegexMagic - Use RegexMagic to generate complete regular expressions to your specifications by using RegexMagic's flexible patterns, instead of the cryptic regex syntax.
Patterns - Patterns is a simple yet powerful tool for working with regular expressions.