regexpviewer is a small app for regular expression experimentation.
Move the mouse over the () matches and see the corresponding text.
Available from http://dedasys.com/freesoftware/applications.html (link broken 2012-11-11 - use http://dedasys.com/freesoftware/files/regexpviewer.tgz instead)
Similar to Visual REGEXP.
EKB I like it! It's simple, with a clean and clear interface.