As you probably know, there is no armour of any kind that the Nameless One could wear in Planescape: Torment. Tattoos act as armour in this game. Some of the tattoos are available only after certain actions have been performed by the Nameless One, which means you'll never be able to see them all at Fell's Tattoo Parlor in the Hive.
Extremist (one of our message boards regulars) has put down all of the tattoos that you can get in the game (and even some that you can't get via regular means) along with their abilities.
If there is a number in parenthesis, it means how many charges you can use when invoking the tattoo's ability. It is noted if invoked effect on statistics is not permanent.
Tattoo of the Warrior - for fighters only: AC +1, STR +1, HP +3
Tattoo of the Supreme Warrior - for fighters only: AC +3, STR +3, HP +9
Tattoo of the Art - for mages only: INT +1, memorize 1 additional spell (level 1 and 2)
Tattoo of the Magi - for mages only: INT +3, doubles all level 1 and 2 spells
Tattoo of the Thief - for thieves only: DEX +1, Locks +5%, PickPocket +5%
Tattoo of the Master Thief - for thieves only: DEX +3, Luck +1, Locks +5%, PickPocket +5%, Traps +5%, Stealth +5%
Tattoo of the Anarchists: Causes Confusion in the enemies (5)
Tattoo of the Betrayer: STR +1, INT +1
Tattoo of the Redeemer: WIS +2, CHR +1, Luck +1
Razor Angel Ink - for non-evil characters only: Invokes: "Protection from Evil" (3)
Tattoo of the Tale-Weaver: CHR +1, Lore +5
Tattoo of Devouring Vermin: Save vs. Poison +1, Resistance: Acid +5%
Tattoo of Sensation - for Sensates only: Damage +1, Suffer +5% from Physical Attacks, THAC0 +1
Tattoo of the Sensates - for Sensates only: Invokes: "Sensory Touch" (13), Lore +3
Tattoo of the Bonesinger: Invokes: "Hold Undead" (6)
Tattoo of the Deceiver: Damage +3, THAC0 +3
Tattoo of the Shattered Lock - for thieves only: Invokes: "Knock" and grants 250 XP when invoked (33)
Tattoo of the Cutpurse - for thieves only: Invokes: "Copper Blessing" and grants 250 XP when invoked (33)
Tattoo of the Shadows - for thieves only: Invokes: "Shroud of Shadows"and grants 250 XP when invoked (33)
Tattoo of the Restless Dead: Invokes: "Bless" (9)
Tattoo of Tenement Shadows - for thieves only: Stealth +15%
Tattoo of Avernus: Resistance: Fire +33% and Magical Fire +33%, Immunity to Panic
Tattoo of the Source - for Godsmen only: CHR +2, Grants 6000 XP when invoked (1)
Tattoo of the Unbroken Circle: Invokes: "Zerthimon's Focus" (3)
Tattoo of the Joining: Invokes: "Friends" (9)
Tattoo of Spite: Invokes: "Tasha's Unbearable Derisive Laughter" (9)
Tattoo of Trist's Savior: Save vs. Paralyzation +3
Tattoo of Justice's Eye: STR +1, Invokes: "Detect Evil" (33)
Tattoo of Death-in-Life - for Nameless One only: Invokes: "Raise Dead" (3)
Tattoo of Grosuk's Demise: Invokes: "Improved Strength" (9)
Tattoo of Sebastion's End: Invokes: "Flamewalk" (9)
Tattoo of Dreams of Es-Annon: Save vs. Spells +1, HP +2
Tattoo of Graves of Es-Annon: Save vs. Death Magic +2, HP +2
Tattoo of Ravel: CHR +1, Immunity to panic
Tattoo of Ravel's Kiss - for Nameless One only: WIS -1, INT -1, STR +2, CON +2, Save vs. Paralyzation +1
Tattoo of the Silver Tongue - for Nameless One only: CHR +2, if invoked temporary CHR +3 (3)
Tattoo of the Black-Barbed Maze - for Nameless One as mage only: Invokes: "Black Barbed Curse" (9)
Tattoo of the Black-Barbed Call - for Nameless One as mage only: Invokes: "Black Barbed Shield" (33)
Tattoo of Annah - for Nameless One as thief only: DEX +1, CHR -1, WIS -1, all thieving abilities +3%
Tattoo of Saving Grace - for Nameless One only: WIS +1, Lore +5, All Saving Throws +1
Tattoo of Logik Cubed - for Nameless One only: If invoked temporary INT +3 and WIS -3 (1)
Tattoo of Ignus - for Nameless One only: CON +1, WIS -1, HP +3, Resistance: Magic -15%, if invoked temp. Resistance to Fire +15% and Magical Fire +15% (3)
Tattoo of the Skull - for Nameless One only: CHR +1, WIS -1, if invoked temporary Save vs. Paralyzation +1 and Luck +1 (3)
Tattoo of Accuracy: THAC0 +1
Tattoo of Bloodletting: Damage +1
Tattoo of Might: STR +1
Tattoo of Greater Might - for fighters only: STR +2
Tattoo of Insight: INT +1
Tattoo of Revelation - for mages only: INT +2
Tattoo of the Spirit: WIS +1
Tattoo of the Soul: WIS +2
Tattoo of Action: DEX +1
Tattoo of Greater Action - for thieves only: DEX +2
Tattoo of Health: CON +1
Tattoo of Greater Health - for fighters only: CON +2
Tattoo of Presence: CHR +1
Tattoo of Greater Presence: CHR +2
Tattoo of Enduring: HP +3
Tattoo of Greater Enduring - for fighters only: HP +9
Tattoo of Warding: AC +1
Tattoo of Greater Warding - for fighters only: AC +2
Tattoo of the the Lost Incarnation - for Nameless One only: Regeneration Rate increased if worn, if invoked 1500 XP (1)
Tattoo of Wasting Darkness - for Nameless One as thief only: CHR -1, AC +1, Stealth +5%, if invoked Stealth +3 and 1500 XP (1)
Tattoo of the Weeping Stones - for Nameless One only: CHR -1, AC +1, Resistance to Cold +10% and Magical Cold +10%, if invoked 1500 XP (1)
Tattoo of Silent Coins: PickPocket +5%, if invoked PickPocket +3% and 1500 XP (1)
The Number of Ku'u Yin - for non-chaotic only: Protection from Chaotic creatures
Symbol of Torment - for Nameless One only: Invokes: "Rune of Torment" (33)