Mailchecker is very fast & very small software (it takes you only 20kB). It's an e-mail notification utility that can check multiple accounts for new mail.

POPLight is an easy to use mailchecker. Just type in your account information and POPLight will check your account within an interval specified by the user. The program can put itself in the system tray and from there it can notify the user by: starting an application, flashing the keyboard lights or playing a WAV file. NEW: Configuration wizard!

MailMagic is a great new email processor featuring mail notification, talking email, spam filtering with delete, flame-back, bounce-back, mailing list manager, talking clock, multilanguage speech sythesisis. Runs as an icon in the system tray.