In alphabetical order, modules that make my life easier or just plain make me happy.

Exception::Class
Simple interface that allows you to quickly put an exception hierarchy together and to easily add attributes and behavior to the classes as necessary.
IO::Wrap
Because it means you can accept any handle-like thing. Makes for nice interfaces.
Module::Build
Easily customizable. I prefer this so much over the alternatives that I no longer include Makefile.PL files in new code.
Module::CoreList
Ah, the fun manipulations you can do when you combine it with PPI. Invaluble when maintaining a non-public CPAN repository.
Perl6::Say
For all that code that can't use 5.10 features yet. No more explicit newlines or unnecessary double-quotes.
Pod::POM::Web
Live, linked, syntax-highlighted, AnnoCPAN integrated, pleasant-to-read, full-text searchable, HTML perldoc? Oh, yes.
PPI
Making your code malliable for over 6 years. I've always considered code "slushy"; this helps keep it that way.
Readonly
Constants that work properly. You definitely want to be using Readonly::XS with this.

Similarly, here are tools I really like.

ack
A better grep than grep. A better find than find. I can't work without it any more; thankfully, I don't have to.
annopod
A better perldoc than perldoc. (In fact, I've got "perldoc" aliased to annopod.) AnnoCPAN comment integration plus no need to use -F any more.
pmtools
I use pmpath, pmvers, and pminst on a daily basis. When your codebase lives in 50+ distributions and you have all the prerequisite third-party modules in a local CPAN repostitory to deal with as well, these are invaluble.
svnnotify
If only the standard Subversion email used this. (Or at least put the log message before the file list.)

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Elliot Shank