There are dozens (or, more likely, hundreds) of providers of free email services. However, the vast majority of them only offer web-based mail, rather than allowing you to use a POP3 client, such as Outlook Express.
The most frequently recommended service which does offer POP3 mail is Google's GMail:
http://mail.google.com/
However, some people don't like the way that Google automatically scans all mail, so that advertising matter can be appended:
http://www.privacyrights.org/ar/GmailLetter.ht m
My own preference is use Gawab. See paragraphs 3, et seq, of my post here for details of how to set up a Gawab account with Outlook Express:
http://www.theanswerbank.co.uk/Technology/Inte rnet/Question407429.html
Both GMail and Gawab are good for setting up 'disposable' email addresses (e.g. when you just need an address to sign up to an offer). I've probably created around 100 addresses with Gawab, although I just use 4 at the moment.
However, you can have up to 5 addresses with Virgin anyway. Click on 'Email addresses', here, for details:
http://www.virgin.net/customers/my_mail/
You might also need some of the information from here:
http://www.virgin.net/helpme/email/outlook6/in dex.html
Chris