Although I mainly do digital art, my favourite medium to work in is actually scratchboard. I was introduced to it in an illustration course a few years ago, and just fell in love with the stuff. Something about putting down ink and then scraping parts off again to produce a full image is just immensely satisfying.
I don’t get many chances to use it, though — the boards are fairly expensive, and I don’t have a decent workspace set up for traditional media at the moment. I’ve tried to get the same effect digitally, but have never found anything with quite the right ‘feel’.
But I picked up a cheap copy of Manga Studio a while back, and it seems to work really well for inking. After a lot of messing with brush settings I think I might actually be getting somewhere.