GoDaddy have what they call a (Unified Communications Certificate) UCC certificate which they claim can be used to:
* Secure up to 100 domain names on one certificate.
* Save money because the cost of one Multiple Domain Certificate, with additional domain names, is less than the cost of individual certificates for each unique domain name.
* Compatible with Microsoft Exchange Server 2007 and Microsoft Communications Server.
* Simplifies the process of managing multiple certificates with varying expiration dates.
Check them out here:
http://www.godaddy.com/gdshop/ssl/ssl.asp?ci=8979