I've been using StartCom for my personal email certificates and also for my domain for SSL for over 2 years now.  They offer a great service, excellent customer service, and very fast turn-around on identity verification during your account setup.  I just read via twitter from @dm_the_company that Microsoft added StartCom to their list of trusted root certificate authorities.  Windows 7 will come out-of-the-box with StartCom as a root CA and Microsoft also has an optional patch available for XP and Vista that can be installed to add the StartCom certificates to those operating systems, which allows those certificates to be recognized by the OS without any extra work done by the user.  Very good news.  I recommend you give them a look if you're in the market for getting a certificate for your domain or personal email.  Also, their Class 1 certificates are free and for minimal cost you can upgrade to Class 2 or 3 validation depending on your needs.