I've seen some kind of overlay thing you can get for CRT monitors to make them touchscreen(I saw this at a movie theater) and I was completely amazed. Well, I want to do this to my LCD monitor. Where can I get one of these devices? Multitouch is a plus, as is Linux support, though neither are absolutely required.
I have no experience in this but the following article from eHow seems promising:
The instructions are explained here: How to Convert an LCD to a Touch Screen
You can google for those touch add-on kits. I came across this, for example.