vSphere is licensed per physical CPU (socket, not core), without restrictions on the amount of physical cores or virtual RAM configured. There are also no license restrictions on the number of virtual machines that a (licensed) host can run.
S&S basic or production (1Year example) - Production (P): 24 Hours/Day 7 Days/Week 365 Days/Year; Basic (B):12 Hours/Day Monday-Friday. Subscription and Support is mandatory. Details and other packages (Acceleration Kits Essential Kits are available). Details here: http://www.vmware.com/files/pdf/vsphere_pricing.pdf and here http://www.vmware.com/products/vsphere/pricing