Samsung Galaxy S4 USB Not Recognized by Windows 7
After searching the Internet for similar issues, I did the following:


I unplugged my phone from the USB cable.
On the home screen, I pressed the bottom left Settings button and chose Settings.
I selected "... More".
I pressed "Developer options" in the list below.
I turned on the Developer options at the top.
Under the Debugging section, I checked "USB debugging".
I reinstalled Samsung Kies.
I started Kies.
After Kies started, I plugged in my phone to the USB cable.


After connecting my phone with Kies running, the Windows Update form appeared and a new entry was in the list.  After the driver installation, everything worked.  I don't even have to run Kies first before connecting my phone to get Windows 7 to recognize it.  It just works.

I don't know exactly what series of events caused this to start working, but now I can actually copy stuff to and from my phone.  (Yay!)