Level 89 Skillbooks Sage/Demon

Brimstone Pit (FB 89 Sage)

Demonic Vexation (level 91, metal, metal immune):
-Demon Plume Shot (Cleric)
-Demon Garrotte (Barbarian)
-Demon Stone Rain (Wizard)
-Sage Ironwood Scarab (Venomancer)
-Sage Tiger Maw (Blademaster)
-Sage Frost Arrow (Archer)

Ethereal Abomination (level 93, no element, random aggro):
-Demon Blazing Arrow (Archer)
-Demon True Form (Barbarian)
-Demon Tiger Maw (Blademaster)
-Sage Great Cyclone (Cleric)
-Sage Fox Form (Venomancer)
-Sage Gush (Wizard)

Fats (level 92, no element, water immune, HP absorb):
-Demon Stomp of the Beast King (Barbarian)
-Demon Frost Arrow (Archer)
-Demon Blessing of the Purehearted (Cleric)
-Sage Venomous Scarab (Venomancer)
-Sage Stone Rain (Wizard)
-Sage Stream Strike (Blademaster)

Eden (FB 89 Demon)

Thousand Year Spirit (level 91, earth, earth immune)
-Demon Venomous Scarab (Venomancer)
-Demon Draw Blood (Blademaster)
-Demon Take Aim (Archer)
-Sage Plume Shot (Cleric)
-Sage True Form (Barbarian)
-Sage Pyrogram (Wizard)

Ninetails (level 92, fire, fire immune)
-Demon Fox Form (Venomancer)
-Demon Stream Strike (Blademaster)
-Demon Pyrogram (Wizard)
-Sage Stomp of Beast King (Barbarian)
-Sage Blessing of the Purehearted (Cleric)
-Sage Take Aim (Archer)

Phlebo (level 93, earth, AoE debuff-amp)
-Demon Great Cyclone (Cleric)
-Demon Ironwood Scarab (Venomancer)
-Demon Gush (Wizard)
-Sage Garrotte (Barbarian)
-Sage Blazing Arrow (Archer)
-Sage Draw Blood (Blademaster)

In short, where to look for books:

Demon Blademaster (2 in Demon FB, 1 in Sage FB):
-Ethereal Abomination (Brim)
-Thousand Year Spirit (Eden)
-Ninetails (Eden)

Sage Blademaster (1 in Demon FB, 2 in Sage FB):
-Demonic Vexation (Brim)
-Fats (Brim)
-Phlebo (Eden)

Demon Wizard (2 in Demon FB, 1 in Sage FB):
-Demonic Vexation (Brim)
-Ninetails (Eden)
-Phlebo (Eden)

Sage Wizard (1 in Demon FB, 2 in Sage FB):
-Thousand Year Spirit (Eden)
-Ethereal Abomination (Brim)
-Fats (Brim)

Demon Archer (1 in Demon FB, 2 in Sage FB):
-Ethereal Abomination (Brim)
-Fats (Brim)
-Thousand Year Spirit (Eden)

Sage Archer (2 in Demon FB, 1 in Sage FB):
-Demonic Vexation (Brim)
-Ninetails (Eden)
-Phlebo (Eden)

Demon Cleric (1 in Demon FB, 2 in Sage FB):
-Demonic Vexation (Brim)
-Fats (Brim)
-Phlebo (Eden)

Sage Cleric (2 in Demon FB, 1 in Sage FB):
-Ethereal Abomination (Brim)
-Ninetails (Eden)
-Thousand Year Spirit (Eden)

Demon Barbarian (all in Sage FB):
-Demonic Vexation (Brim)
-Ethereal Abomination (Brim)
-Fats (Brim)

Sage Barbarian (all in Demon FB):
-Thousand Year Spirit (Eden)
-Ninetails (Eden)
-Phlebo (Eden)

Demon Venomancer (all in Demon FB):
-Thousand Year Spirit (Eden)
-Ninetails (Eden)
-Phlebo (Eden)

Sage Venomancer (all in Sage FB):
-Demonic Vexation (Brim)
-Ethereal Abomination (Brim)
-Fats (Brim)

Source: www.ecatomb.net