Common Books
[Informational] Aedra and Daedra
[Informational] Ancestors and the Dunmer
[Religious, Temple] Homilies of Blessed Almalexia
[Religious, Temple] Lives of the Saints
[Informational] Overview of Gods and Worship
[Informational] Reflections on Cult Worship
[Religious, Temple] Saryoni's Sermons
[Informational] Special Flora of Tamriel
Spirit of Nirn
[Religious, Temple] The Anticipations
[Religious, Temple] The Cantatas of Vivec
The Changed Ones
[Religious, Temple] The Consolations of Prayer
[Religious, Temple] The Book of Dawn and Dusk
[Religious, Temple] The Doors of the Spirit
[Religious, Temple] The Pilgrim's Path
The Monomyth
[Informational] The Vagaries of Magicka
[Informational] Varieties of Faith
[Religious, Temple] Vivec and Mephala

Uncommon Books
[Informational, Scholarly, Dwemer] Antecedants of Dwemer Law
[Poetry] Ashland Hymns
[Cult] Blapshemous Revenants
[Cult] Book of Life and Service
[Cult] Book of Rest and Endings
[Religious, Daedra] Invocation of Azura
[Historical] Poison Song, Book I
[Historical] Poison Song, Book II
[Historical] Poison Song, Book III
[Historical] Poison Song, Book IV
[Historical] Poison Song, Book V
[Historical] Poison Song, Book VI
[Historical] Poison Song, Book VII
The Arcturian Heresy
The Blue Book of Riddles
[Poetry] The Five Far Stars
[Informational] The Real Nerevar
The Red Book of Riddles
The Yellow Book of Riddles
[Informational] The War of the First Council
[Informational] Vampires of Vvardenfell, Vol. I
Words of Clan Mother Ahnissi
[Poetry] Words of the Wind

Somewhat Rare Books
[Cult, Necromancy] Arkay the Enemy
[Skill] Bone, Part I
[Skill] Bone, Part II
[Skill] Breathing Water
[Skill] Chance's Folly
[Historical, Dwemer] Chronicles of Nchuleft
[Necromancy] Corpse Preparation I
[Necromancy] Corpse Preparation II
[Necromancy] Corpse Preparation III
[Informational, Personal Story] Confessions of a Skooma-Eater
[Profane?] Hanin's Wake
[Necromancy] Legions of the Dead
[Informational, Scholarly, Dwemer] Guylaine's Architecture
[Historical, Dwemer] Nchunak's Fire and Faith
[Skill] Realizations of Acrobacy
[Skill] Smuggler's Island
[Skill] The Axe Man
[Skill] The Cake and the Diamond
The Final Lesson
[Skill] The Four Suitors of Bentiah
[Informational, Great House Telvanni] The Brown Book of _E___
[Skill] The Hope of the Redoran
[Skill] The Marksmanship Lesson
[Skill] The Prayers of Baranat
[Informational, Great House Redoran] The Red Book of _E___
[Skill] The Wraith's Wedding Dowry
[Informational, Great House Hlaalu] The Yellow Book of _E___
[Skill] Unnamed Book
Where Were You When the Dragon Broke?

Rare Books
Charwich-Koniinge Letters, Letter I
Charwich-Koniinge Letters, Letter II
Charwich-Koniinge Letters, Letter III
Charwich-Koniinge Letters, Letter IV
[Religious, Temple] The 36 Lessons of Vivec, Sermon 1
[Religious, Temple] The 36 Lessons of Vivec, Sermon 2
[Religious, Temple] The 36 Lessons of Vivec, Sermon 3
[Religious, Temple] The 36 Lessons of Vivec, Sermon 4
[Religious, Temple] The 36 Lessons of Vivec, Sermon 5
[Religious, Temple] The 36 Lessons of Vivec, Sermon 6
[Religious, Temple] The 36 Lessons of Vivec, Sermon 7
[Religious, Temple] The 36 Lessons of Vivec, Sermon 8
[Religious, Temple] The 36 Lessons of Vivec, Sermon 9
[Religious, Temple] The 36 Lessons of Vivec, Sermon 10
[Religious, Temple] The 36 Lessons of Vivec, Sermon 11
[Religious, Temple] The 36 Lessons of Vivec, Sermon 12
[Religious, Temple] The 36 Lessons of Vivec, Sermon 13
[Religious, Temple] The 36 Lessons of Vivec, Sermon 14
[Religious, Temple] The 36 Lessons of Vivec, Sermon 15
[Religious, Temple] The 36 Lessons of Vivec, Sermon 16
[Religious, Temple] The 36 Lessons of Vivec, Sermon 17
[Religious, Temple] The 36 Lessons of Vivec, Sermon 19
[Religious, Temple] The 36 Lessons of Vivec, Sermon 20
[Religious, Temple] The 36 Lessons of Vivec, Sermon 21
[Religious, Temple] The 36 Lessons of Vivec, Sermon 22
[Religious, Temple] The 36 Lessons of Vivec, Sermon 23
[Religious, Temple] The 36 Lessons of Vivec, Sermon 24
[Religious, Temple] The 36 Lessons of Vivec, Sermon 25
[Religious, Temple] The 36 Lessons of Vivec, Sermon 26
[Religious, Temple] The 36 Lessons of Vivec, Sermon 27
[Religious, Temple] The 36 Lessons of Vivec, Sermon 28
[Religious, Temple] The 36 Lessons of Vivec, Sermon 29
[Religious, Temple] The 36 Lessons of Vivec, Sermon 30
[Religious, Temple] The 36 Lessons of Vivec, Sermon 31
[Religious, Temple] The 36 Lessons of Vivec, Sermon 32
[Religious, Temple] The 36 Lessons of Vivec, Sermon 33
[Religious, Temple] The 36 Lessons of Vivec, Sermon 34
[Religious, Temple] The 36 Lessons of Vivec, Sermon 35
[Religious, Temple] The 36 Lessons of Vivec, Sermon 36

Illegal/Forbidden Books
[Religious, Temple] The 36 Lessons of Vivec, Sermon 0
[Religious, Temple] The 36 Lessons of Vivec, Sermon 18
[Informational, Religious, Temple] The Progress of Truth
[Informational] Vampires of Vvardenfell, Vol. II

Unique Books
Boethiah's Pillow Book
[Joke] Capn's Guide to the Fishy Stick
[Journal, Forbidden] Galur Rithari's Papers
[Joke] No-H's Picture Book of Wood
Samar Starlover's Journal
Tal Marog Ker's Researchers

Likely Outdated/Invalid Books
[Informational, Temple] Fellowship of the Temple
[Informational, Fighters Guild] Fighters Guild Charter
[Informational, Imperial Cult] For My Gods and Emperor
[Informational, Great House Hlaalu] Grasping Fortune
[Informational] Great Houses of Morrowind
[Informational] Guide to Ald'Ruhn
[Informational] Guide to Balmora
[Informational] Guide to Sadrith Mora
[Informational] Guide to Vivec
[Informational] Guide to Vvardenfell
[Informational, Imperial Legion] Ordo Legionis
[Informational, Great House Telvanni] The Affairs of Wizards
[Informational] The Alchemist's Formulary
[Informational, Morag Tong] The Black Gloves
[Informational, Great House Redoran] The True Noble's Code

Common: You'll find these all the time. Mostly informational and Temple books.
Uncommon: Not as commonplace as, er, common, but you'll run into them often.
Somewhat Rare: Contains most of the skill-teaching books. Also a lot of necromancy books. I'd say no more than 15-18 of each should be present.
Rare: Contains the 36 Lessons of Vivec and the Charwich-Koniinge Letters. No more than 2 or 3 should be around.
Illegal/Forbidden: 36 Lessons of Vivec, Sermon 0 is unique. 36 Lessons of Vivec, Sermon 18 should only appear once or twice and not in public areas. The Progress of Truth should only appear one or two times. Vampires of Vvardenfell, Vol. II should appear no more than four times.
Unique: These books should only appear once each.
Outdated/Invalid: These books are not up-to-date or aren't valid in Oblivion. They probably shouldn't be used.

The words in the brackets are basic categorizations of the book based on its content. You'll find books most "Temple"-marked books in Tribunal Temples. You won't, for instance, find a "Red Book of _E___" in a Hlaalu area, either, since the Red Book is Redoran.