AFAIK all certificates are pretty much equal as far as security goes (make sure to choose at least 1024-bit encryption strength in your certificate request)
The biggest difference is in the verification process, the cheap certs only do an email check, others (such as the Extended Validation certs) need much more proof, but they also cost much more.
I get mine from
https://www.cheapssls.com/ (usually just the COMODO Positive SSL for $8.95)