PNF (Pen And Free Co.) released the Duo, so you can turn your laptop into a touchscreen without ripping it apart. You just install the receiving station on top or on the side of your screen, define the area you want to use as a tablet and that’s all. However, you have to use a stylus to operate. The laptop version supports up to 15.4″, the monitor version to 22″. Oh and it is actually pretty cheap: 44$ for a tablet seems to be a deal. 

For details and such, click here.