Not sure if anyone has heard of it yet..
3Doodler is a 3D printing Pen.
https://www.youtube.com/watch?v=emUlHFWcHck
Home 3D printing might be a long way from being commercially available but this is cheap as heck for small bits.
I can imagine this being great for doing a lot of things including terrain making as shown in some videos.
Just thought I link it in case there are interested people out there