My custom vertical 3x5" notebook. The rings open like a binder so that you can add or remove pages easily. It just uses standard index cards that I hole punched. : r notebooks Amazon.com : 3x5 Lined Index Cards with Ring Binder Holder and Dividers, 100 Ruled Cards, Blue : Office Products Bovi's Genuine Leather Hasp Business Card and Credit Card Holder Hide & Drink, Leather Mini Briefcase Card Holder, Holds Up to 10 Cards Plus Folded Bills, Case, Cash Organizer, Handmade Slim Leather Credit Card Organizer Leather Business Credit Card Holder Wallet Wood Brown Staples Index Card Holder for 3" x 5" Cards, 100 Card Capacity, Assorted (ST50992 CC) Staples