I love notebooks and Moleskines are one of the best choices when it comes to scribbling your thoughts.
After using the blank and ruled versions, I find I much prefer the large, soft-covered Moleskine with grids. I have untidy handwriting and the grids help me write neater. It also allows me to make more precise field sketches at work. I also prefer the soft cover as it makes it easier to bring around.
The best place to buy them is online at Books Depository, which provides free international shipping without a minimum purchase.