Hi Jimil.. As mentioned in the pervious post from vsphere 5 there is no ESX and its only ESXi from now on..BUt still its good know the difference for awareness.
Basic differences are as said in ESX services console is there is is Linux based one and in ESXi there is no services console.
Also ESX all the operation are carried out to VMkernel via services console because vpxa is installed in services consle.
But in ESXI there vpxa is directly on vmkernel, so the performance is much improved as it talks directly to vmkernel.
Refer the below link to detailed explaination.
http://www.vmware.com/products/vsphere/esxi-and-esx/compare.html
Also refer the link given for feature difference between esx and esxi..