Linode actually has Xen, but it's been in beta for a while. I haven't tried it yet, so I can't compare, but once you register for it in the CP it will migrate y

Linode actually has Xen, but it's been in beta for a while. I haven't tried it yet, so I can't compare, but once you register for it in the CP it will migrate your data/IP to the Xen platform without any changes on your end.