How do you Handle SSLs?

Currently we use Thawte SSL123's for our e-commerce clients, but we are just finding it is just more trouble than it should be getting the certificates issues and/or re-issued. We're looking for an SSL provider with good browser support (we don't want to have to mess with certificate chaining), a simple API that would allow us to script the entire provisioning process so we could allow clients to enter their data, could write a script to gen the csr and could automatically apply for and install the SSL without manual intervention. Anyone got any suggestions?