A while back I published an article on partitioning your ESX host. This was based on 3.5, and of course with vSphere this has slightly changed. Let me start by quoting a section from the install and configure guide.
You cannot define the sizes of the /boot, vmkcore, and /vmfs partitions when you use the graphical or text installation modes. You can define these partition sizes when you do a scripted installation.
The ESX boot disk requires 1.25GB of free space and includes the /boot and vmkcore partitions. The /boot partition alone requires 1100MB.
The reason for this is the fact that the service console is a VMDK. This VMDK is stored on the local VMFS volume by default in the following location: esxconsole-<system-uuid>/esxconsole.vmdk. By the way, “/boot” has been increased as a “safety net” for future upgrades to ESX(i).
So for the manual installations there are three partitions less to worry about. I would advise to use the following sizes for the rest of the partitions, and I would also recommend to rename the local VMFS partition during installation. The default name is “Storage1″, my recommendation would be “<hostname>-localstorage”.
/ - 5120MB
Swap - 1600MB
/var - 4096MB
/home - 2048MB
/opt - 2048MB
/tmp - 2048MB
With the disk sizes these days you should have more than enough space for a roughly 18GB for ESX in total.