http://www.startssl.com/
I had heard about some other free or trial certs before, however apparently startssl certs are trusted by fully patched versions of xp (optional update), vista (optional update) and windows 7 (out of the box).
With snooping tools so easy as firefox plugins this makes taking the extra step to secure personal sites feasible.
Yeah, I found out about that a week or so ago, and have used a few of their free certs already. I'll probably end up paying for their validated certs too at some point.