- Book of Holding - This very heavy tome appears to be a collection of works by various hands from various times but resting a mundane book on top of it will cause that book to be added to its pages. It never changes size and appears to have infinite room for more new works.. Titled Praecepta ad Filium by Simplicius Porphyrogenitus.
- Book of Many Compartments - It has 600 pages and 100 hidden cut outs. You must remember the pages that small items may be hidden on, otherwise it appears a normal work of natural history. Titled Memorabilia by Diodorus the Elder
- Dandolo's Fechtbuch - Studying a section will grant a benefit to any combats the next day, but you can choose only one section to study: Offense: +1, Defense: +1, Caution: reduced fumbles, Boldness: extended critical range.
- Book of Translating - Appears to be a dry record of commercial deals and political agreements made by different pairs of speakers. But if two people touch the book while talking it will record that conversation in the book. Conversations appear to be in whatever language the reader understands best. Titled Accords of the Caravan Princes by Harun al-Hafiz.
- Book of Rehearsing - Appears to be small philosphical dialogues in which a person entreats another in different ways to different results. Say the name of a person and then say something to them. These will appear in the book along with that persons probable responses (a way to rehearse important npc interactions). Titled The Dialectics by Proclus of Tatos.
- Book of Snakes - Contains hundreds of swatches of reptile skin. Poorly labelled but experience will show it contains rattlesnake, spitting cobra, python, flying snakes and even a basilisk. Once a day, touching a swatch will cause the book to turn into that reptile and the toucher will be able to communicate with that snake.
The other idea was to have a set of volumes that improve effectiveness as you find more of them. I think one way to do this is have 4 books for making a poison or potion that break down like this 1) finding and harvesting ingredients 2) preparing ingredients 3) cooking and processing ingredients together 4) storing and applying.
Players might sell any of them for gold, but if you set it up right they might have better and better chances of successfully completing the poison/potion. Could be a mini-game or just abstract bonuses. I was thinking a Chinese lich could have written 10,000 of these and the series is titled After Drinking a Golden Potion.