My case:
2 vCPU and 2 GB memory ram for AppServer (running java generally over guest OS Linux)
1 vCPU and 1 GB for WebServer (running Apache over guest OS Linux)
With respect guest OS Windows... generally 2 vCPU and memory sizing is calculated aproximated according to the application that will running...
More memory o vCPU is evaluated according to both the resources available on the Hots ESX and if the application actually needs it according to what specified by the supplier.
ESX Host configuration:
4 Blades HP BL 460c G6
8 cores - 2.99 GHZ
64 GB Ram
Total Virtual Machines : 52
But considerate that applications running in virtual machines, is not same run one java instance over VM of 2 vCPU with 2 GB memory that SQL Server 2000 with transactional Database.
Greetings