I recently had to do some shopping for a SSL certificate for my startup Stratismo (I linked to it incase anyone wants to see the actual certificate). Obviously I wanted one that was widely supported and didn't really want to pay a ridiculous amount for it.
So shopping around I landed on RapidSSL's site. RapidSSL has a program where you can switch to them if you have a competitor's certificate. On top of that they also give you a free year. All of this for free. The program details are here:
I just happened to have a Comodo certificate so I gave this a test run. The Comodo certificate had some issues because of the number of intermediate certificates I had to include. While this shouldn't cause problems in theory in reality it is just one more thing to deal with.
So what I did was apply for RapidSSL. They ended up giving me one of their SSL certificates for free after verifying I had a Comodo SSL certificate. They also extended the validation by a year so basically I got two years for $10. RapidSSL certificates are also signed by Equifax which is installed on almost every browser.
Overall a great deal.