Make computer go to sleep after USB phone charging is complete

I think a less complicated solution would be charging your phone through an outlet by using the included charging adapter or a powered USB hub. That way you don't have an entire computer running just to charge your iPhone.

I am currently waiting to receive my pre-order on 3 TruePower UCS Power Outlet with USB ports so I can plug devices in at night without needed a special adapter or a computer.

Our custom TruePower power outlet solution includes two Universal Serial Bus (USB) charge ports in addition to the two standard three prong power outlet ports.

Perfect for charging any USB powered device including- mobile, iPod, iPhone, PDA, MP3, PSP, MP4 player & digital camera.

Installation: This item can be installed on any existing wall outlet.

We will have an installation video available shortly so that you can see exactly what is involved and if this is something you feel comfortable doing on your own or if you will need assistance.

Please also note that the USB ports only draw power when something is physically connected to the port. We didn't want a vampire port that continually sucks and wastes power when not in use so this was one of the features on the top of our priority list during the design phase.

Similar to @Jared's (admittedly "cooler" answer) you can buy a simple USB wall charger for a few dollars. They are cheap, and simple. Or, you might do like this guy's Instructable and DIY your own.

This doesn't in any way actually answer your question of how to make your PC shut down after the phone is finished charging via its USB cable, but it does seem rather superfluous to run an entire PC just to charge the phone via the 5V line on its USB hub. :)

Check whether your computer's BIOS has an always-on USB option. This provides power while the computer is asleep, so you can put it to sleep immediately while the phone charges. Some computers have yellow USB ports for this purpose. (I'm not sure if they have them on desktops, though.)