This is my Rhodia No14 notepad (11x17cm). One of my current favourites. These little beauties are made in France and available in a few UK stores. Blackwells and Paperchase (in Borders) sell them but there are also a few online suppliers with wider ranges.
It's a strange design in a way. The staples at the top mean that you have to fold the cover up or round the back of the notebook but it does this easily. You can use it portrait or landscape and each sheet is perforated for easy removal. They are inexpensive but the quality of the paper is fantastic. I usually write in pencil which writes smoothly over the surface but I've also written with my Stabilo Sensor (in the photo) and other gel type pens-all write smoothly with no bleed through. The red and black band is a velcro cable tie that I've put round it which slides down the notebook to both hold the notebook shut and hold my pen.
The pages of the number 14 will also fit into a personal size Filofax or a Compact size Franklin Covey binder. A bit wider than both these page sizes but great for adding notes in.
There are a variety of sizes, from wee cute ones that would fit in your trouser pocket to A4 size for fitting into your folio. They come in plain, lined and 5x5 grid. I've taken a shine to the grid version.
The Rhodia site has an English version so have a look at what they have.