Here are some of the servers I will be running (note this is for an office of 10 individuals, so we won't be pounding them)... rough ideas on what I'm looking to allocate:

Domain Controller

(1) 30GB Drive

Web Server

(2) 30GB Drives

Database Server

(2) 30GB Drive

(1) 50GB Drive

Exchange Server

(1) 30GB Drive

(1) 50GB Drive