I've been frustrated for some time about not having POP access anymore on Yahoo! Mail, and having to manually forward any important mail I receive to my home system. The answer is a great app by Lou Forlini called Mail Forward.
MailForward allows multiple accounts, automated retrieval, can leave mail on the server, and forwards arrive w/ the original sender identified in the "From" header, so any sorting rules will still apply.
[Editor's note: I haven't tested this program, but it sounds very useful if you're one of those who uses the numerous web-only free email services.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20021213113938291