Probably all of you, when looking for Storage vMotion permissions, will find KB:
http://kb.vmware.com/kb/1011345
This KB is at the first place in all searches issued from google...:)
All would be great, but it is actually no longer applicable to vCenter versions 4.x and 5.x and is related only to RCLI.
To create role which allows user to perform Storage vMotion you can copy standard Read-Only role (or VM User/VM Power User role -> depends on access to Virtual Machines you would like to give to users) and add following permissions:
Datastore -> Allocate Space
Datastore -> Browse Datastore
Datastore -> Remove File
Datastore -> Update Virtual Machine Files
Resources -> Migrate
Resources -> Relocate
Virtual Machine -> Provisioning
Virtual Machine
-> Allow Disk Access
Virtual Machine
-> Allow Read-Only Disk Access
Newly created role now allows you to perform Storage vMotion.