Get All Users List 

http://your-site-name/_vti_bin/ListData.svc/UserInformationList

Get A User By Account or Any Other Property

http://your-site-name/_vti_bin/ListData.svc/UserInformationList?$filter=Account eq ‘contoso\administrator’&$select=Id,Name

Get Users by Content Type

http://your-site-name/_vti_bin/ListData.svc/UserInformationList? $filter=ContentType eq ‘Person’