vSphere Replication is part of vSphere ESXi 5.1 and is available at all licensing levels except Free and Essentials. vSphere Replication works at the host level to replicate virtual machines from host to host without any reliance on a storage system. The replication could be from host to host at the same local, or to a host at a different site provide basic disaster recovery for your virtual machines.
http://www.vmware.com/products/datacenter-virtualization/vsphere/replication.html
Site Recovery Manager is a fully featured DR application which can utilize vSphere Replication or native SAN replication. SRM takes DR to the next level in that you can perform tasks such as:
- creating a DR plan which includes aspects of which VMs to protect, changing IP addresses when a VM is brought online in a DR situation, and controlling the order of VMs being brought online
- automate DR failover and fallback
- perform DR testing without disruption to production servers
http://www.vmware.com/products/site-recovery-manager/features.html