Well obviously, Hotmail is big one!! That is the one I mainly use and my personal favourite.
There is also;
Gmail - Gmail is the Google approach to email, chat and social networking. 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 - 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 - 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
Yahoo! Mail - Yahoo! Mail is your ubiquitous email program on the web and mobile devices with unlimited storage, SMS texting and instant messaging to boot.
While Yahoo! Mail is generally a joy to use, free-form labeling and smart folders would be nice, and the spam filter could catch junk even more effectively.
Gawab.com - Gawab.com is a speedy, stable and very usable free email service with 10 GB online space, POP and IMAP access as well as many a web-based goodie.
It's a pity Gawab.com's IMAP implementation does not give you access to labels, and full message search is missing from the web interface.
Inbox.com - 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.
Fastmail - FastMail is a great free email service with IMAP access, useful features, and a stellar web interface.
It's a pity FastMail does not offer truly effective spam filtering for free accounts, and more storage space for all users.
Windows Live Mail - 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.
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 IMAP access to all online folders would be nice.
Yahoo! Mail Classic - 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.
BigString.com - 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.
Lavabit - Lavabit nets you a solid, secure and privacy-conscious email account which you can access in your email program using POP or IMAP and in your browser using a rudimentary web interface.
It's a pity Lavabit restricts statistical spam filtering to paid accounts and lacks a fully fledged web interface.
Zapak Mail - Zapak Mail is a bare-bones free email service with unlimited storage and POP access to boot. With the exception of some background images, Zapak Mail offers no frills and does not help much with handling mail efficiently
Myspace Mail - MySpace Mail adds an email address to your social network so you can exchange messages with everybody, not just MySpace members.
Unlimited storage lets you keep all the mail you like, but don't count on MySpace Mail helping you organize the messages — or your address book. It's also a pity MySpace Mail does not offer POP or IMAP access and cannot retrieve mail from external accounts.
HotPOP - HotPOP offers free, reliable email accounts you can use with any email program using POP3 and SMTP. In addition, HotPOP lets you forward incoming messages to multiple other addresses.
Unfortunately, HotPOP lacks IMAP access and a web-based email interface and is a bit short on storage space.
My Way Mail - My Way Mail is a clean, fast and fun (though not particularly advanced) free email service.
It lacks secure messaging and other advanced, non-essential features, though.
Care2 Email - Care2 E-mail provides solid free email with an environmental conscience. The spam filters and editing gimmicks in Care2 E-mail are ni