I ran across a great free project today at:
http://cert.startcom.org

This group allows you to get FREE SSL certificates for your website.  Like anything free, there’s a catch.  They’re not in the list of root certificates, yet.  They claim that they’ve passed an audit by Microsoft to be added to the list of root certificates, but we’ll see if that actually happens.  All this means is that you have to have users import the root certificate (simple web-based process) to prevent them from getting the obnoxious message about the certificate not being trusted.  It’s as simple as providing the clients with a link to:
http://cert.startcom.org/index.php?app=109
which will automitically prompt them to import the certificate, and then bounce them back to the site where they came from.

In my case, I’m using this for Outlook Web Access, and found a great tutorial that walked me through everything I needed to do at:
http://www.msexchange.org/tutorials/SSL-Enabling-OWA-2003-Using-Free-3rdParty-Certificate.html