This instructable shows how to easily control 110Vac from a serial output port on a PC. The serial port I used was a USB type. Any standard serial port should work.
The idea is to connect the DTR (data terminal ready) pin from the PC serial port to a Crydom solid-state relay. The Crydom relay accepts a control signal of 3 to 32 volts to turn on the solid-state relay. The Crydom relay can also handle up to -32 volts on the control input to the relay. See attached datasheet.
Under normally conditions the DTR signal switches between +10 volts and -10 volts. This works out perfectly for the Crydom relay. The Crydom relay turns on at anything above 3 volts. Any voltage below 1 volt is guaranteed to turn off the relay. So, using the +10 to -10 volts of the DTR signal is perfect. The Crydom relay has a maximum load of 2mA on the DTR signal.
Switching the DTR under program control is also really easy. I've attached a little Python script that toggles the DTR pin every couple of seconds. The Python script is only 16 lines long!
To make the Python code work you will need to add an extra little package to Python called PySerial. I've also attached the windows installer for PySerial to this instructable. With a quick Google search, you can find PySerial on Source Forge easily too.