Craig I use Clustered.Net for all my hosting and I cannot speak highly enough of them, they are not the cheapest (you get what you pay for with hosting in my experience) but their tech support is fantastic and nothing is to much trouble for them. In fact I am in the middle of upgrading my server right now !
My view is that you cannot take a chance with ecommerce and I want a host I KNOW I can rely on.
I also provide individual SSL Certs for each site, again it is a relatively small outlay for peace of mind.