In the Web and in different books everybody can find smth like "connon regex lists" containig dozens of reallife regular expressions simple enough to be understood by everybody.

There are also lists of useful and complex regexes that are hard to understand. In particular, Regexp::Common contains a number of useful regexes, both simple and complex.

Also, Jeffrey Friedl's Mastering Regular Expressions has examples of large, complex regexes (one generated one to match an email address that is about a page long IIRC).