Recommendation for Regex editor?

By far, the best tool for the job is RegExr.

The link above will take you to the online version, which is awesome and definitely the best RegEx tool I've ever used.

If you're looking for something you can install in Ubuntu, then try the desktop version, which is an Adobe Air application:

Kodos is an application to aid in the creation and debugging of regular expressions in python. The GUI for Kodos should eliminate the need for using the python interpreter for regex design in most instances.

Homepage: http://kodos.sourceforge.net/

Or online tool: http://www.regextester.com/

visual-regexp still works, and is in the Ubuntu repository. Unfortunately, the name does not start with "regex", so later on you will think, "Oh yeah, what was that regex editor I installed, type "reg", get nothing, go doing a websearch, and ending up here all over again. Also, (because it's Tk-based?), pasting from your paste buffer into the pattern window doesn't seem to work as expected.

Kodos was a wonderful tool, but unfortunately, neither RegExr nor Kodos runs (without great effort) on Ubuntu 12.10+; Kodos has not been upgraded to QT4, and Adobe Air no longer supports Linux.