To get the maximum productivity I have found that a Moleskin notebook with no lines is the best place to create ideas. Any sort of lines will limit you drawings and sketches. It take some time getting used to not having any lines. However, once you get used to it, you will write straight.
Plain notebook, you can get it in many different sizes. Choose the heavy weight paper. If you use fountain pens it will shine through.
If you are in working with stories and doing story telling for your presentations, this is a must have: Storyboard notebook. It looks funny in the beginning. However, it forces you to think in scenarios rather than getting stuck in your old tracks of thoughts.
Best of luck!