Active Directory – “Computers”

We are doing spring cleaning of our Active Directory and wondering if there is a utility which will help to find out if a computer is no longer active on our network. We have “pinged”, however it hasn’t been fail-safe, and it’s too time-consuming for the number of computers in question. We’d like to remove some of the computers from Active Directory, however haven’t found a way to automatically locate this type of info. Any suggestions as to utilities or scripts would be greatly appreciated. Thank you.