I had always been wondering what is the problem with these email providers, that they don't let me view my emails over HTTPS. One of the main reasons I could think of was the increased load on the web servers where the HTTP connection terminates. They will have to spend extra CPU cycles to encrypt/decrypt the incoming and outgoing data. Similar load will be incurred on the user's machine as well.
But Google provides mail over HTTPS. And that is seriously a good news. To access your email over HTTPS, instead of typing www.gmail.com, type "https://mail.google.com".
Oh BTW, it is only the traffic comes from Google mail server to your desktop that is encrypted. Still the traffic between the mail servers go in unencrypted form. For e.g., if you are sending an email from your Google mail account to some account in Yahoo!, the mail will be sent in unencrypted form from Google server to the Yahoo! mail server.
Added on 07/29/2008: A friend of mine working in Google told me even better option. Once you login, you go to Settings and make "Browser connection:" to be "Always use https". Thats even better!