Here’s a neat concept: a sort of modular notebook system in which you can combine various paper types into one big notebook by slotting their covers together, made by StartHere.

Here’s a description of the starter set you can order:

We’ve put together our favorite items, chosen to give you a complete system that allows for functionality, personalization, and flexibility for your ideal organization. Set includes: grid, lined w/ 5 tabs, and 3-level linkable notebooks + one self-adhesive pocket, one self-adhesive color tabs, and one decorative spine adhesive. Interior pages are all 100% recycled paper. Covers are 50% to 100% recycled paper. Biodegradable laminate provides a layer of protection and durability. Patented front cover pocket linking system. One interior pocket.
Size 5×7

You can also choose your own combination of the individual components. You can mix lined paper, graph paper, tabbed sections, planner pages, etc, into one big uber-notebook of your own design.

Pretty cool! But I wish they had size options other than 5×7.