PerlBuilder
( http://www.solutionsoft.com/perl.htm ) is an integrated development environment for Windows that supports Perl development.
visiPerl+
( http://helpconsulting.net/visiperl/ ) From Help Consulting, for Windows.
OptiPerl
( http://www.optiperl.com/ ) is a Windows IDE with simulated CGI environment, including debugger and syntax highlighting editor.
For Windows there's also the CodeMagicCD
( http://www.codemagiccd.com/ ) Collection of various programming tools for Windows: Perl (5.005_03), TclTk, Python, GNU programming tools, REBOL, wxWindows toolkit, the MinGW GNU C/C++ compiler, DJGPP GNU C/C++ compiler, Cint C interpreter, YaBasic.
For editors: if you're on Unix you probably have vi or a vi clone already, and possibly an emacs too, so you may not need to download anything. In any emacs the cperl-mode (M-x cperl-mode) gives you perhaps the best available Perl editing mode in any editor.
If you are using Windows, you can use any editor that lets you work with plain text, such as NotePad or WordPad. Word processors, such as Microsoft Word or WordPerfect, typically do not work since they insert all sorts of behind-the-scenes information, although some allow you to save files as "Text Only". You can also download text editors designed specifically for programming, such as Textpad ( http://www.textpad.com/ ) and UltraEdit ( http://www.ultraedit.com/ ), among others.
If you are using Mac OS, the same concerns apply. MacPerl (for Classic environments) comes with a simple editor. Popular external editors are BBEdit ( http://www.bbedit.com/ ) or Alpha ( http://www.kelehers.org/alpha/ ). Mac OS X users can use Unix editors as well.