I've got a real weakness for Earthworks’ Journals. I've been using their beautiful leather notebooks for many years as the place where I dump most of my words. Earthworks is a small firm - a husband and wife team - from Northampton, UK; a town known for its (sadly much diminished) footwear and leather industries.
The thickness of the leather immediately strikes you when you pick up the journal. It's similar to what you'd expect to find on a well-made boot; extremely thick and tough. You could chuck the journal into a bag or drop it from a tall building without too much concern. Like most leather products, these journals look better as they age. My current notebook, an A5 journal, has become more supple over the year-or-so that I've been using it. The scuffs, scars and knocks it has endured make it look unique as an object, but demonstrate that it is primarily a functional object. This is an object to use, not to treasure.
The paper is superb. It's a little more creamy and off-white than most mass-produced journals. While this compromises it for sketching, it's far easier on the eye, especially in bright environments. The paper is archival quality, meaning that it'll probably outlive you. I find that it's rough enough to handle pencils but smooth and thick enough to take a fountain pen. However it might not be absorbant enough if you use a medium nib or thin ink. The sheafs are bound with a thick chord to the spine of the book; its not quite as polished or tight as mass-produced journals. However, I like the rustic look and it gives the book a more substantial feeling. A downside of stiching paper to thick leather is that the book doesn't like to lay flat, especially when the leather is new and firm. It's tolerable when handwriting or drawing but it can make typing up your notes quite inconvenient unless you can weigh it down.
I tend to buy one Earthworks journal for each of my big writing projects. The physical uniqueness that it develops provides a tactile connection to the project. Forgive me if I sound a little esoteric but it's like a physical totem of the words it contains. When your notebook or journal is also a pleasant object, it adds a tactile, almost visceral dimension to writing; a connection that would otherwise be lacking. It helps to build an emotional connection to the project. Handling the book, fiddling with the leather and - being honest - flaunting it a little, gives me something to look forward to when I'm struggling to motivate myself to write. That's quite important!