Free Web based E-mail  is available from so many sources, it would be impossible to list them all here.  The concept of Web Based Email is very sound:

• You can access your email from any computer that has internet access (just remember your account name and password)
• Supposedly, it's an account you can use "for life" - move, change your internet provider, cancel your AOL account (for example), and your web based email address is still valid.  Note:  This will only be true as long as the free email provider is around, so I would suggest you choose carefully.
• Your identity is even more "anonymous" if you so choose using a Web Based service rather than your Internet Provider email address, particularly if your Internet Provider is "local".

Note:  Many "Free" Web based E-mail  services also offer upgrades available for monthly or annual fees.  So far, I haven't seen any that are really worth paying for - as long as I maintain a POP3 email service as well.

I have NOT tried all of the following services, but they are some of the leaders in Free Web Based Email (also listed due to my belief in their longevity):

Netscape Netcenter - this is a good one.  It includes an excellent version of "when.com's" calendar merged with free email.  Pretty good home page too!

Yahoo - part of the popular search engine site. 

Excite - and yet another solid search engine related email provider with a wonderful browser Home Page.  Voice mail available at no extra charge.

HotMail - part of the msn's offering.  Hotmail's features are great - even allowing you to download the mail right into Outlook Express!  Just as an aside, I've heard that there are over 40,000,000 HotMail users.

ZapZone - I really like this deal, because it offers more than just mail.  Previously known as "what you seek briefcase",  you can Communicate with others (send and receive email), Organize your life (schedule group activities and meetings), Share information with friends and family (almost like having a personal website).  All of this plus 15 MB of storage space. And it's completely FREE!

MailCity - The first I signed up for, and i'm still a faithful user.  Has been acquired (and improved) by Lycos.

AngelFire - I see them used quite a bit (no personal experience)

Mail.com - No personal experience - over 5 million users; cool email address <s>

Tripod.com - more well known for their free websites, they offer free email as well.

You still want more to choose from?  Try the Free Email Providers Guide.. they have a huge list :-)