Having one location to check all of your email accounts via your desktop is always a good thing.  There are many email managers to choose from including Outlook and Thunderbird.  Being able to check your email from Webmail accounts sometimes requires additional cost such as with Yahoo Plus.  Speaking of Yahoo, The Geek has a great tutorial on checking your Yahoo email in Thunderbird using YPOPS! Another utility to keep tabs on your Yahoo as well as other webmail accounts is POP Peeper.  POP Peeper works with POP3, IMAP (including GMail, AOL, AIM, Netscape, FastMail), SMTP, GMail, HotmailMSNLiveMail, Yahoo, Mail.com, MyWay, Excite, Lycos.com, RediffMail, Juno, and NetZero. Pop Peeper is a fresh and unique way to check your email via the desktop.  The main purpose is to sit in your Taskbar and notify you of email messages, but it is almost a fully functional email client unto its own.  POP Peeper can also be run as a portable application which can be password protected.  Installation is extremely easy as a Wizard launches for easy setup.

Wizard

Navigating through the Wizard is extremely straight forward, enter one to as many email accounts as you want.  Including an option to automatically import your accounts.

setup accout

There are also very cool skins for new email notifications such as this iphone notification.  Like most email clients you are able to setup and choose how often email accounts are checked, set up rules for certain messages, and access a handy address book.

gphone

Make sure and have automatic updates checked because there are new improvements happening at a rapid rate.

auto updates

I have found this to be a very useful application.  Although I don't see it replacing Thunderbird for me in the immediate future, there is definitely some promising things happening with POP Peeper