The Secure Pages module
http://drupal.org/project/securepages
A small process which will redirect the the required pages to a SSL version of the page.
So you make sure the user is running on a secure page when they are creating/editing content, viewing user details, or administering the site.
Make sure that your web server has SSL enabled and you Drupal installation has been configured to support SSL access
I have used this on a 4.7 Drupal site and drive standard (http) traffic to one server and SSL (https) traffic to a different server. This way authenticated traffic which is more intensive will not hinder unauthenticated traffic which in my case was the bulk of requests. It can also be used on the same server such that you only SSL the pages that need it.