I use gmail as my email service and I use mozilla thunderbird as my email client although I do like Microsoft Outlook 2007 so I might switch over to that.
I use Yahoo! Mail. Outlook is common, mostly at schools because the email network uses it. Personally I like Mozilla Thunderbird over Microsoft Outlook.
I use Outlook 2007.... very glitchy... I like the 2003 version alot better because of the stability... but i'm just to lazy to fix it. 2007 works okay... a little slow but hey... all I ever get in my e-mail is spam so I rarely check it.