SearchMyFiles - Alternative to the standard Search For Files And Folders module of Windows. Duplicates search is also supported.

RegExr - RegExr.com is an online tool to learn, build, and test Regular Expressions.

dnGREP - dnGrep allows you to search across files with easy-to-read results.

Expresso - The award-winning Expresso editor is equally suitable as a teaching tool for the beginning user of regular expressions or as a full-featured development environment for the experienced programmer with an extensive knowledge of regular expressions.

PowerGREP - Quickly search through large numbers of files on your PC or network using powerful text patterns to find exactly the information you want. Search and replace with plain text or regular expressions to maintain web sites, source code, reports, ...

rubular - A ruby based regular expression editor