Another good source is the Perl Cookbook, Chapter 6. While it obviously cannot cover as much in one chapter as the Mastering Regular Expressions book, the chapter is excellent with many "recipes" and a good style that goes beyond the information in Programming Perl. Plus, you'll find the book invaluable for other things as well. Highly recommended. Available, of course, from O'Reilly:

Perl Cookbook

Update: Better yet, buy it through the unholy alliance of Fatbrain and Perlmonks here: Perl Cookbook :)