I use CGI::Applicaiton::ValidateRM, the nice thing about it is that it also calls HTML::FillInForm to fill back the submitted parameters. Of course, the code in CGI::Applicaiton::ValideRM is only about 20 lines using Data::FormValidator and HTML::FillInForm, so you can do everything with those two modules yourself.

By the way, before I learnt these, I was using java Struts, the fill-parameter-back and error handling is one of the things I liked. It's amazing to see that there are still lots of sites out there that don't do this: you lose all your parameters if one is missing.