I LOVE index cards. When I lived in the US, I would routinely make a trip to the bookstore just to pick up more index cards, the better to process my ideas. It's much less intimidating to look at a blank index card than it is to look at a blank sheet of paper, and there's a limit to how much you can sensibly write on them. Super-portable, too: you can keep a small stack in your pocket, no problem at all.
However, I've always had a nagging feeling that it's a bit wasteful to keep using and disposing of bits of card, no matter how small. If only there was some way to reuse rather than recycle...
Which is where the Noteboard comes in. It's a cross between notecards and a whiteboard. A laminated, fold-up whiteboard.
I'm impressed with it. One side of the board is clear, and the other has various grids (squares and hexagons); it's all packaged up in a small black bag which doubles as a board-wipe. There's a pen included, too. Size-wise, it's a six-by-five grid of cards (about 90cm by 50cm).
My only problems with it are problems of physics and biology: although the pen is as fine-tipped as is practical, there's a limit to how small you can write and draw in ink on laminate, which means I can't fit as much on a card as I'm used to with a pencil; also, because I'm left-handed, I tend to smudge my writing (which is why I normally use a pencil!).
The Noteboard is a good, solid product, and very useful for peripatetic tutors or anyone who goes to MathsJam. It retails for £10 + p&p.
(Disclosure: The Noteboard people did invite me to review their product, but only after I bought it.)