Journaling Arts is a great resource for all sorts of journals and planners. Their shop is organized by type of book: writing, art, travel, planners and more. I especially like the category for Journals for Fountain Pens. You can also search by brand and Journaling Arts stocks a dizzying selection of Moleskine products. Journaling Arts also keeps a blog which is a good resource for detailed product information and techniques for creative journaling.
(tip via Jennifer — thanks!)