I've been using Google's GMAIL for a little while and really like it. It does very good on spam and its interface keeps conversation threads together nicely. And since its relatively new, there are plenty of good email addresses available.

Recently they have been adding features and disk space like crazy. Its still free and they are up to 2GB of space for each mailbox.

I have 50 invitations for accounts left (its still by invitation only). If you are interested, send me an email and I will forward an invite to you.