I think it's inevitable that we'll end up covering books for third-party games on Sega systems. There's loads, which is why until now the focus has been on Sega developed/published-games, but some are so rare it would be a shame not to document them in some form. Whether they'll all get pages, I can't say.
Some of this content might be destined for Retro CDN.
Japan
Master System
Mega Drive
Mega-CD
Game Gear
Saturn
Dreamcast
Multi-platform
US
Master System
Mega Drive
Ballz 3D Official Strategy Guide
Disney's Pocahontas Official Game Guide
Double Dragon V: The Shadow Falls Official Strategy Guide
Mortal Kombat II Official Power Play Guide
NBA Jam Official Player's Guide
Official Game Book: Toy Story
Official Game Secrets: Boogerman
Official Mortal Kombat 3 Fighters' Kompanion
Official Mortal Kombat 3 Pocket Kodes
Official NBA Hang Time Player's Guide
Official Player's Guide: Super Street Fighter II
Street Fighter II' Turbo Hyper Fighting Strategy Guide
Totally Unauthorized Guide to Super Street Fighter II
Troy Aikman Football Official Playbook
Mega-CD
Dungeon Master II Official Strategy Guide
Lunar: The Silver Star - The Official Strategy Guide
Rise of the Dragon Hintbook for Sega CD
Vay for Sega CD: The Official Strategy Guide
Game Gear
Saturn
Croc: Legend of the Gobbos Official Game Secrets
GameFan's Die Hard Trilogy Strategy Guide
Gex Official Game Secrets
Night Warriors (GameFan books)
Totally Unauthorized Hexen Strategy Guide
Dreamcast
Industrial Spy: Operation Espionage: The Official Strategy Guide
NFL Blitz 2000 Official Strategy Guide
Official Blue Stinger Strategy Guide
Prima's Official Strategy Guide: Centipede
Prima's Official Strategy Guide: Dead or Alive 2
Prima's Official Strategy Guide: Draconus Cult of the Wyrm
Prima's Official Strategy Guide: Evolution 2
Prima's Official Strategy Guide: Half-Life
Prima's Official Strategy Guide: Legacy of Kain: Soul Reaver
Prima's Official Strategy Guide: NFL Blitz 2000
Prima's Official Strategy Guide: Omikron: The Nomad Soul
Prima's Official Strategy Guide: Power Stone
Prima's Official Strategy Guide: Rayman 2: The Great Escape
Prima's Official Strategy Guide: Ready 2 Rumble Boxing
Prima's Official Strategy Guide: Resident Evil: Code Veronica
Prima's Official Strategy Guide: Silver
Prima's Official Strategy Guide: SoulCalibur
Prima's Official Strategy Guide: Star Wars Demolition
Prima's Official Strategy Guide: Star Wars Episode I Racer
Prima's Official Strategy Guide: Super Magnetic Neo
Prima's Official Strategy Guide: Tomb Raider Chronicles
Prima's Official Strategy Guide: Tomb Raider: The Last Revelation
Prima's Official Strategy Guide: Tom Clancy's Rainbow Six
Prima's Official Strategy Guide: Tom Clancy's Rainbow Six Rogue Spear
Prima's Official Strategy Guide: Toy Commander
Prima's Official Strategy Guide: Ultimate Fighting Championship
Ready 2 Rumble Boxing Official Strategy Guide
Slave Zero Official Strategy Guide
Street Fighter Alpha 3 Official Fighting Guide
Multi-platform
Action Series Strategies for Mortal Kombat
GamePro's Official Mortal Kombat Strategy Guide
GamePro Official Player's Guide: Batman Forever: The Video Game
GamePro Presents Primal Rage: Official Player's Guide
Judge Dredd: The Official Strategy Guide
The Lion King OFficial Game Book
Mortal Kombat Fighter's Kompanion
Mortal Kombat II Official Fighter's Kompanion
Mortal Kombat II Official Player's Guide
Mortal Kombat 3 Player's Guide
MTV's Beavis and Butthead Cheater's Guide
NBA Jam: Tournament Edition Super Book
Official Player's Guide: NBA Jam: Tournament Edition
Official Player's Guide: Pitfall: The Mayan Adventure
Official Player's Guide: Road Rash 3
Official Ultimate Mortal Kombat 3 Fighter's Kompanion
Official Ultimate Mortal Kombat 3 Pocket Kodes
Totally Unauthorized Primal Rage
UK
Master System
Mega Drive
Street Fighter II' Expert Player's Handbook
Super Street Fighter II Official Players Guide (Capcom/Gamepro ISSN 1357-6135)
Mega-CD
Game Gear
Saturn
Dreamcast
Official Acclaim Strategy Guide: Fur Fighters
France
Dreamcast
Le Guied Officiel: Rayman 2: The Great Escape
Specific games
Earthworm Jim 2: Official Game Secrets
GamePro Presents: Primal Rage Official Player's Guide