The question is, what is a computer? The consensus here is that a "computer" does not need to have all the neccessary parts. So I am just trying to figure out where to draw the line.
For this market I think the least we could expect would be case, power supply, motherboard, memory, processor, hard drive, optical drive, video, the standard ports, and OS.
Keyboard and mouse are optional, although included ones are so cheap that they should probably ship with any new system just in case the buyer doesn't already have them (I'm not dumping my Logitech keyboard/mouse for what comes with any new computer, even a Mac). Monitor is definitely optional, as lots of people are just replacing their current machines, and it's easy to order a monitor with the computer.