Sherwood,
If you're running OS X, by all means consider the bundled Mail application. It does POP, IMAP, and is well behaved. The 10.2 upgrade will bring some more features, and excellent integration with a new system wide address book.
If you are still on OS 9, I'd say check out Eudora (
www.eudora.com) or Mailsmith (
www.barebones.com). Depends on your needs though...