I'm using a StartSSL free SSL certificate on my home PFsense portal. I noticed it doesn't play nice with Firefox, but IE authenticates to it fine.
I would highly suggest a paid SSL certificate for a business environment.http://www.cheapssls.com/
Comodo is $8 a year and RapidSSL is $9. I'd go with RapidSSL, Comodo's CEO is an idiot.