There are a couple on CPAN -- the source of all good things Perl. I've used Mail::POP3Client in the past to write a rudimentary spam filter (before I changed ISPs ;-). It worked OK, though I didn't really stress it.

I noticed that NET::POP3 is from Graham Barr, so it's likely to be pretty good. It appears to be a standard module for 5.7.2, so it'll likely be on the next stable release as well.

HTH

Update
Learned how to point links to CPAN! Whoo-hoo!