TP-Link Smart Power Outlet Plug for $28.
Normally at least $35.
This is the HS110 model that lets you turn on/off the power plug from your smartphone or tablet, and monitors the energy usage.
We have the HS100 model which works similarly, without the energy usage monitoring.
It works really well when there is a device you want to turn on/off from power, without physically unplugging it.