Gmail is the Google approach to email, chat and social networking. Free online storage allows you to collect all your messages and see them in context without effort.
Windows Live Hotmail is a free email service that gives you 5 GB (and growing) of online storage, fast search, solid security, POP access and an interface easy as a desktop email program.
Yahoo! Mail is your ubiquitous email program on the web and mobile devices with unlimited storage, SMS texting, social networking and instant messaging to boot.
AIM Mail, AOL's free web-based email service, shines with unlimited online storage, very good spam protection and a rich, easy to use interface.