Gmail is the Google approach to email and chat. Practically unlimited free online storage allows you to collect all your messages, and Gmail’s simple but very smart interface lets you find them precisely and see them in context without effort. POP and powerful IMAP access bring Gmail to any email program or device.
Gmail puts contextual advertising next to the emails you read.

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. Unfortunately, AIM Mail lacks a bit in productivity (no labels, smart folders and message threading), but makes up for some of that with very functional IMAP (as well as POP) access.

GMX Mail is a reliable email service filtered well of spam and viruses whose 5 GB of online storage you can use not only through a rich web interface but also via POP or IMAP from a desktop email program.
More and smarter ways to organize mail could be nice.

Zenbe organizes your emails and attachments (from Zenbe and existing POP accounts) with labels and search and integrates calendar, to-do list, twitter and Facebook updates, too.
With a focus on elegant simplicity, Zenbe provides many sweet shortcuts but also shows quirks and omissions in others. The spam filter is good, but it would be great if IMAP access was possible for all folders (not just the inbox).

Inbox.com not only gives you 5 GB to store your mail online but also a highly polished, fast and functional way to access it via either the web (including speedy search, free-form labels and reading mail by conversation) or through POP in your email program. Unfortunately, IMAP access is not supported by Inbox.com, and its tools for organizing mail could be improved with smart or self-teaching folders.

Gawab.com is a speedy, stable and very usable free email service with 2 GB online space, POP access and many a web-based goodie.
It’s a pity Gawab.com lacks IMAP access and full message search.

FastMail is a great free email service with IMAP access, useful features, one of the best web-based email interfaces and few ads.

Yahoo! Mail Classic is a comfortable, reliable and secure email service with unlimited storage. A pretty good spam filter keeps the junk out, and you can send rich emails using Yahoo! Mail’s HTML editor.

Windows Live Hotmail is a free email service that gives you a 5 GB of online storage, fast search, solid security and an interface easy as a desktop email program.
When it comes to organizing mail, Windows Live Hotmail does not go beyond folders (to saved searches and tags, for example), its spam filter could be more effective, and POP or IMAP access are missing.

BigString.com is a free 2 GB email service that includes rich secure and certified mail services and lets you password-protect, expire or edit sent messages, for example.
Unfortunately, BigString.com is not equally well equipped for handling incoming mail and lacks organizing tools.