Did you forget Javascript? I don't know many web shops that can get away without using at least some form of Javascript now adays.

I would throw in templating languages as well. HTML::Mason and Template::Toolkit, are both similiar but not exactly pure Perl. The have their own quirks that you have to learn.

The final thing I wanted to throw in custom parsers. Poorly written ones are more cryptic than trying to decode a MD5 hash by hand...