Brush markers in Moleskine sketchbook.
The brush pen doesn't respond to pressure like a real brush, and doesn't produce the surprise and beauty of a real brush either - but also, hey, no blobs! And so transportable. Actually, it's a glorified marker, but a very seductive instrument because so smooth and easy to use, and I like the chunky lines because my tendency is to a nervy line, and a thin point makes that too scratchy sometimes. But with a brush pen, you can't really get fine detail, should you want to. Great colours though. I love using various tones of the same colour, especially the shades of grey.