Web-Based

Another.com
Over 6000 domains to choose from. It has many unique features including letting you have up to 20 addresses all operating from the same in-box.
http://www.another.com/

Apple .Mac
Fee-based service, pay for a year at a time. Email, web storage, offsite virtual hard drive, various free tools and files. 60-day free trial available.
http://www.apple.com/dotmac/

Bigfoot
Variously priced webmail packages with integrated anti-spam and email forwarding services.
http://webmail.bigfoot.com/

Dreamersi.net
Offers e-mail services for small-to medium-sized businesses that are not ready to have an in-house server or do not want an internal mail server.
http://www.dreamersi.net

E-MailAnywhere.com
Has many of the standard features, though lacks filtering. Provides a "Briefcase" which allows storage of files on provider's server for future use.
http://www.e-mailanywhere.com/

Lisa.com
An e-mail forwarding service, not a regular e-mail account. There is no inbox, or other features.
http://www.lisa.com/lisaemail.html

Mail.CHEK.com
MailCHEK specializes in custom e-mail templates for brands, companies, and organizations.
http://mail.chek.com/

MauiMail.com
E-mail access via standard mail clients, or the convenience of web based mail.
http://www.mauimail.com/

Plug-in email systems
Plug-in email systems for businesses, web sites, and educational institutions.
http://www.ownmail.com/

Showbiz.com
Offers web-based e-mail accounts for yearly fee with personalized address books.
http://www.showbiz.com/webmail

Your mail is here, come and get it!
Microsoft corporate weblog about online e-mail offerings.
http://mailcall.spaces.live.com/