Lately, for me:

• File::Finder -- filter chaining all so much more elegant than File::Find
• Proc::Background -- makes me able to forget the differences of process execution between Win32 and other OS's
• File::Repl -- kind of cool non-local rsync-like module
• DBD::Pg -- the want for it never goes away :)
• WWW:Mechanize -- just played with it shortly, but definitely funky in a good way
• YAML -- actual concise hand-editable serialization! Yes!
• XML::Simple -- when folks aren't cool enough to use YAML :)
• Tk -- looks aside, you can't beat a clean GUI API
• MIDI::Simple -- has some fun examples, though my Computer Music for-fun projects aren't really going anywhere
• PAR -- solid gold for program distribution. Convert perl to binary, "essentially".