PopTray checks POP accounts for new mail periodically — but it is not limited to POP accounts, there are plug-ins for IMAP and Hotmail,Gmail etc. Join the forum discussion on this post
POP Peeper is an email notifier that runs in your Windows task bar and alerts you when you have new e-mail. Join the forum discussion on this post
Password Safe is a free application for keeping or creating safely passwords and protect sensible data with a very strong encryption (256-bit), dual encryption that includes both 'Blowfish' and 'Rijndael' with 256 bits each. Join the forum discussion on this post
Multi Email Notifier will notify you for all your Gmail, Hotmail, Live, Rocketmail, Yahoo and POP3 accounts.
Google Email Uploader is a simple tool that helps you import email messages and contacts from your current desktop client to Gmail, in just a few simple steps.