Targus has its new Touch Pen for Windows 8 here at CES 2013, with a grand aim of turning any monitor into a pen-capable display. It works via USB and a small receiver that attaches to the side of a laptop or display. The Touch Pen mimics touch actions in Windows 8, allowing you to quickly navigate the tiled interface.
The pen has a soft tip so it won't scratch your screen, but I found that it's definitely not a perfected technology just yet. The vast majority of touch actions and strokes with the pen registered well, but as soon as I reached to the very edges of the display it simply didn't recognise the input. Swipes from the edge will display the Windows 8 Charms, but a swipe from the top failed to close the apps. Targus tells me that it's still working on the Touch Pen and that it will not ship until around Q2 this year.