Sudo !! equivalent in PowerShell

$^ is a variable that expands to the last executed Powershell command.

You can run a command as another user using runas, so the following works:

runas /user:domain\administrator $^

To shorten that up a bit, you can do some magic with aliases. Take a look at this Technet article for more info.

EDIT: One caveat - $^ only executes the first command in a pipeline or multi-command line. If you need to redo an entire command that is peppered with pipes or semicolons, use Invoke-History instead (which defaults to the last full command in its entirety).