$filter = (new-object Amazon.EC2.Model.Filter).WithName('tag:Name').WithValue('YourInstanceName') (Get-EC2Instance -Filter $filter -Region 'us-east-1').RunningInstance | % { Stop-EC2Instance $_.InstanceId -Region 'us-east-1'}
AWS can do for a dollar what other Cloud can do for two.
$filter = (new-object Amazon.EC2.Model.Filter).WithName('tag:Name').WithValue('YourInstanceName') (Get-EC2Instance -Filter $filter -Region 'us-east-1').RunningInstance | % { Stop-EC2Instance $_.InstanceId -Region 'us-east-1'}