A good comparison can be found here: http://www.thomas-krenn.com/en/wiki/VMware_vSphere_5_Editions_Overview
And a nice one-stop shop on all the feature names linked to thier information can be found in this Google Doc: https://docs.google.com/spreadsheet/ccc?key=0AkDahcUh0bJkdElsVXdfeUNlN3d4dWRDdWRKTFNld2c&usp=sharing#gid=2
At the end of the day though, if you want to move a running VM from one datastore to another, you have to be at "Standard"...none of the Essentails levels come with that.