Python Regular Expressions
Regular Expressions Cheat Sheet from DaveChild. A quick reference guide for regular expressions (regex), including symbols, ranges, grouping, assertions and some sample patterns to get you started.
Regular-Expressions.info - Regex Tutorial, Examples and Reference - Regexp Patterns
Always need a Regular Expressions Cheat Sheet! Cheatography.com
Perl Regular Expressions Cheat Sheet
Regular Expression in a Regular Expression Validator.
Regular Expression Cheat Sheet