It is hard to define the perfect notebook. I have two that I like and would recommend for different reasons. The first is an obvious choice, the Moleskine journal. I especially like the smallest size, which will fit into your pocket. I keep 2 at any given time: one for day to day notes and a second for the good stuff– great ideas, perspective changing insights, advice, etc.
The second kind of notebook is a Bienfang note/sketch book. The top half is blank and the bottom is ruled, perfect for planning. My rule when using this notebook is to illustrate an idea on top and describe it on the bottom. It forces you to use both sides of the brain and think of common problems in new ways. Its great for having on your desk and taking to meetings.