Compare the SSL Providers side by side
We completed the purchase, install and testing of a cert from GeoTrust. Everything went off without a hitch and we had the cert in ~15-20 minutes.
In addition, GeoTrust let's you 'transfer' a cert. If you have an existing cert you can give a URL or paste a certificate data when you purchase a cert from Geotrust. They reduce the cert price to $119 and they extend the certificate expiration by the number of months left on your existing cert.
This worked to my client's advantage because they are retiring a Linux box with a Thwate cert that didn't expire until next June, so they bought a new one year cert that won't expire until 2005.
They validate the cert two ways, sending an e-mail to one of the domain registration accounts (another reason for companies NOT to have third parties register domain names in their behalf) and with a phone call. The phone call is automated, you must enter a four digit code which is displayed during the registration process and record your name (through the phone).
Other companies have a more manual process (FAX, human intervention,etc) which may be more through, but takes 2-5 working days which can cause problems when your on a client site trying to get something working.