Email notification at it's best - POP Peeper

For any person maintaining more than a couple of email accounts, this is an indispensible tool. It’s a notifier that sits in your Windows task bar and alerts you when you have new email. It works with POP3 accounts (including GMail) as well as web mail account like Hotmail, Yahoo, Rediffmail etc.

You can read mails (along with the attachments) and delete them from within the interface without having to open the browser or your mail client. It can even send email and it quite handy for sending quick replies.

It has a bunch of plugins, all of which are useful. The FAQ provides important information about setting up some of the accounts (especially GMail since it requires the SSL plugin). The developer is currently working on Bayesian spam filters for the mailboxes as well.

All this completely free of cost, so grab it!