Shortest:

“The Modern Discussion About Bioethics”
by Prof. Hojo of Shinra – Foreword by Lucrecia V.

“How I Quit Smoking”
by Cid Highwind

“A Guide to Personality”
by FF1 Team

“Black Materia: An In-Depth Study Based On My Pre-Gaea Crater Observations”
by Cloud Strife

“How To Get The Girl Of Your Dreams”
by Kain Highwind and Vincent Valentine

Longest:

“Home-made Remedies Against Insomnia”
by Vincent Valentine

“The Problem Of Life After Death: Does Such a Thing Actually Exist?”
by Auron

“The Gentle Art of Making Enemies”
by various authors – Foreword by Garland

“Find Yourself”
by Cloud Strife

“The Midgets: A New Wonderful World Unveiled”
by FF3 team

“The Rocky Horror Picture Show: Thorough Analysis of a Masterwork From a Real Lover”
by Kuja

“The Revised and Improved Swearword Dictionary”
by B. Wallace, C. Highwind and Z. Dincht

“A Guide To Woman Self-Defense”
by Rydia and Yang’s Wife