I am fond of SourceForge's PerlIDE (Perl Integrated Development Environment).

I have also used the more powerful Komodo by ActiveState (who also provide the open source versions of Perl); but in its open source form it is pretty limited; you have to pay a modest amount to get the more powerful one.

PerlIDE has a good debugger and the ability to set watch variables, break points, etc. It also has a nice feature (not unusual for most IDE's, but nice nonetheless) that once you reach a breakpoint, just mousing over a variable anywhere in the code that has already run will give you a pop-up bubble that shows its value. That means that many of the quick checks can be done without having to set watch variables.

The IDE is easy to use (it has documentation, but I have found that it is not all that great and the package is largely intuitive and self-explanatory so the weak documentation is not much of a problem. The only drawback that I have found is that I can't figure out how (if there is a way at all) to easily do command-line running of scripts from within the IDE. Komodo, on the other hand, supports such a capability very nicely.