Windows account ending with $

That's the computer account. When a computer joins a domain it has to have an account associated with it in order to apply policy settings. This gets created automatically when the computer joins.

From Microsoft's technet article on accounts:

Computer accounts

Every computer running Windows NT, Windows 2000, Windows XP, or a server running Windows Server 2003 that joins a domain has a computer account. Similar to user accounts, computer accounts provide a means for authenticating and auditing computer access to the network and to domain resources. Each computer account must be unique.