Some thoughts are:

• A theme based article - based around solving common real world problems with REs, perhaps looking at Regexp::Common for theme material. Select the themes to highlight whatever you want.
• Common gotchas and pitfalls with Perl REs
• Regex optimisation, perhaps looking at parsing records and including use of $/ and split to simplify the task. (ie REs + pick the right tool for the job and use all the tools you need)
• C/GNU REs vs Perl REs - know your engine.