VMware released ESX 3.5 in late 2007. Some of its new features included Storage vMotion, SATA drive support, 10 GbE support, Jumbo Frames support and the VMware update manager. You can read more about ESX 3.5 here:
The latest version of ESX is included in the vSphere 4.1 platform, which VMware released in July 2010. VSphere 4.1 is the last version that will add any new features to the ESX hypervisor; from here on out, VMware will be focusing solely on the ESXi hypervisor.