This is a step-by-step howto to help you migrate a CentOS/RHEL 5 VM with xen-tools installed in XenServer 5.5 to VMWare ESX.
I have done this last year when I migrated from XS 5.5 to ESX 4. It should also work on ESXi 5 and CentOS/RHEL 6. The concept is still the same but the version of kernels, vmware converter and hypervisors will be different so please post here to share the knowledge if you do a migration from later versions.