[Indemaijinj]

Some spoilers are bound to appear:
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Fighter, barbarian and (quite weirdly) monk:
D'Arnise Keep. Get Nalia to appoint you to regent of the Keep after you defeated Tor'Gal.

Ranger:
Merella's cabin. Get it (along with the responsibilities of Merella) as gratitude for defeating the Shadelord. (Umar Hills quest).

Paladin:
Room in the Radiand Heart HQ. Get it after saving Garren Windspear's child (Windspear Hills quest).

Thief:
Mae'Var's Guildhall. Get it after you have defeated Mae'Var for Renal Bloodscalp.

Bard:
The Five Flagons inn and playhouse. Get it after doing the Planar Prison quest.

Wizard and sorcerer:
The Planar Sphere: Get it after completing the Planar Sphere quest (Involving Valygar in some way or another).

Cleric:
Clerics are a special case: Your alignment will determine your stronghold.
Good Cleric: Temple of Lathander.
Neutral Cleric: Temple of Helm.
Evil Cleric: Temple of Talos.
The prequisite quest is in all circumstances the Unseeing Eye quest.