You don't want to use one of those bulky e-mail clients and the only thing you want is to be warned when you have new e-mail. So here you are! Also, that's not all of course, it also shows you the sender, subject and beginning of the body of message.

Email Checker Features
Stays out of way in the system tray.
Provides pop up window when email is found.
Shows who wrote email, subject and first several lines of each email.
It can serve up to several thousand POP3 servers.