1. Hardware : any Good dual processor speed will do the job
2.Ram : it will depends what kind of service it will run, such as how many hits will get, how many software it will run but 3-4GB ram would be sufficient for a average sige of website
3. Infrastrucure :
a) redundancy
b) at least 1 static ip ( if you dont do dns management)
c) 2 isp line ( in case if one isp goes down)
d) Aircondition to cool the server
e) Good uplink and downlink, if your uplink and downlink is less then user will have to wait for gettign connection from yoru site
if you add all together the amount of money you will spent, its easy to have Dedicated server rented from a data centre ..
