The idea here is to maximize critical damage multiplier on an unarmed character. To achieve this we will be taking the overwhelming critical feat, devastating critical from the LD fate, and be in Earth III stance for a grand total of 19-20 X5 criticals.* Secondary focus will be on additional +[W] multipliers and multiple sources of seeker to get the most bang per buck for those 19-20 criticals. I should point out that while the focus here is on critcal damage, the damage per attack on 2-18 rolls will still be quite satisfactory. There's also still the good old Touch of Death for DPS as well.

*Note that I am fairly certain that not all of these currently work as intended, but I think they should all stack together once functional.

In addition, we will single-handedly be able to reduce enemy fortification by up to 60% with the combined application of Improved Sunder (-10%), Touch of Despair (-25%) and Precision (-25%). After all, those X5 crits wont do us any good if they're all blocked by fortification.

Finally, while the primary focus is strength and damage, you can still pull off a reasonably effective stunning fist DC for when fighting trash.

Melee builds benefit greatly from gaining a few past lives, and this one is no exception. I am presuming a 36-point character with access to the monk past-life and +3 dex tome (though I assume +3 in all stats). It can be done with 32 points and +2 tomes as well, but the damage and stunning capabilities go down quite a bit as result.

Without further ado, the build:

Code:
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Level 20 Lawful Neutral Half-Orc Male
(6 Fighter \ 12 Monk \ 2 Ranger) 
Hit Points: 324
Spell Points: 0 
BAB: 17\17\22\27\27
Fortitude: 19
Reflex: 16
Will: 15

                  Starting          Feat/Enhancement
Abilities        Base Stats          Modified Stats
(36 Point)       (Level 1)             (Level 20)
Strength             20                    32
Dexterity            14                    17
Constitution         14                    17
Intelligence          6                     9
Wisdom               15                    20
Charisma              6                     9

Tomes Used
+1 Tome of Strength used at level 3
+1 Tome of Dexterity used at level 3
+1 Tome of Constitution used at level 3
+1 Tome of Intelligence used at level 3
+1 Tome of Wisdom used at level 3
+1 Tome of Charisma used at level 3
+2 Tome of Strength used at level 7
+2 Tome of Dexterity used at level 7
+2 Tome of Constitution used at level 7
+2 Tome of Intelligence used at level 7
+2 Tome of Wisdom used at level 7
+2 Tome of Charisma used at level 7
+3 Tome of Strength used at level 11
+3 Tome of Dexterity used at level 11
+3 Tome of Constitution used at level 11
+3 Tome of Intelligence used at level 11
+3 Tome of Wisdom used at level 11
+3 Tome of Charisma used at level 11

                  Starting          Feat/Enhancement
                 Base Skills         Modified Skills
Skills           (Level 1)            (Level 20)
Balance               2                     7
Bluff                -2                     0
Concentration         2                     8
Diplomacy            -2                     0
Disable Device       n/a                   n/a
Haggle               -2                    -1
Heal                  2                     5
Hide                  2                     7
Intimidate           -2                     0
Jump                  5                    13
Listen                2                     5
Move Silently         2                     3
Open Lock             n/a                   n/a
Perform              n/a                   n/a
Repair               -2                    -1
Search               -2                    -1
Spot                  2                     5
Swim                  5                    11
Tumble                n/a                   n/a
Use Magic Device     n/a                   n/a

Level 1 (Ranger)
Feat: (Favored Enemy) Favored Enemy: Evil Outsider
Feat: (Past Life) Past Life: Fighter
Feat: (Past Life) Past Life: Fighter
Feat: (Past Life) Past Life: Fighter
Feat: (Past Life) Past Life: Monk
Feat: (Past Life) Past Life: Monk
Feat: (Past Life) Past Life: Paladin
Feat: (Selected) Toughness


Level 2 (Ranger)


Level 3 (Monk)
Feat: (Selected) Past Life: Disciple of the Fist
Feat: (Monk Bonus) Stunning Fist


Level 4 (Monk)
Ability Raise: STR
Feat: (Monk Bonus) Power Attack


Level 5 (Monk)
Feat: (Monk Path) Path of Inevitable Dominion: Fists of Darkness


Level 6 (Monk)
Feat: (Selected) Precision


Level 7 (Monk)


Level 8 (Monk)
Ability Raise: STR
Feat: (Monk Bonus) Dodge


Level 9 (Fighter)
Feat: (Fighter Bonus) Improved Sunder
Feat: (Selected) Weapon Focus: Bludgeoning Weapons


Level 10 (Fighter)
Feat: (Fighter Bonus) Improved Critical: Bludgeoning Weapons


Level 11 (Fighter)


Level 12 (Fighter)
Ability Raise: STR
Feat: (Fighter Bonus) Improved Two Weapon Fighting
Feat: (Selected) Weapon Specialization: Bludgeoning Weapons


Level 13 (Fighter)


Level 14 (Fighter)
Feat: (Fighter Bonus) Greater Two Weapon Fighting


Level 15 (Monk)
Feat: (Selected) Cleave


Level 16 (Monk)
Ability Raise: STR


Level 17 (Monk)


Level 18 (Monk)
Feat: (Selected) Great Cleave


Level 19 (Monk)


Level 20 (Monk)
Ability Raise: STR
Enhancement: Fighter Attack Boost I
Enhancement: Fighter Attack Boost II
Enhancement: Fighter Haste Boost I
Enhancement: Fighter Haste Boost II
Enhancement: Ranger Sprint Boost I
Enhancement: Kensei Unarmed Mastery I
Enhancement: Fighter Critical Accuracy I
Enhancement: Fighter Critical Accuracy II
Enhancement: Fighter Kensei I
Enhancement: Fighter Strategy (Sunder) I
Enhancement: Fighter Strategy (Sunder) II
Enhancement: Orcish Extra Action Boost I
Enhancement: Orcish Power Attack I
Enhancement: Orcish Power Attack II
Enhancement: Orcish Strength I
Enhancement: Orcish Strength II
Enhancement: Static Charge
Enhancement: Way of the Patient Tortoise I
Enhancement: Way of the Patient Tortoise II
Enhancement: Touch of Death
Enhancement: Porous Soul
Enhancement: All-Consuming Flame
Enhancement: Monk Improved Recovery I
Enhancement: Monk Ninja Spy I
Enhancement: Monk Ninja Spy II
Enhancement: Void Strike I
Enhancement: Winter's Touch
Enhancement: Adept of Rock
Enhancement: Master of Stone
Enhancement: Racial Toughness I
Enhancement: Racial Toughness II
Enhancement: Ranger Favored Damage I
Enhancement: Improved Jump I
Enhancement: Improved Jump II
Enhancement: Improved Tumble I
Enhancement: Improved Tumble II
Enhancement: Fighter Strength I
Enhancement: Fighter Strength II
Enhancement: Monk Wisdom I
Enhancement: Monk Wisdom II
Enhancement: Fighter Toughness I
Enhancement: Fighter Toughness II
Epic destiny: Legendary Dreadnaught
Sundering swing (1) (currently doesn't work unarmed but should be fixed)
Legendary tactics (3)
Extra action boost (1)
Improved power attack
Damage boost (2)
Momentum Swing (1)
Lay waste
Critical damage (3)
Strength increase X2
Advancing Blows
Devastating critical
Masters Blitz

Epic feats are Overwhelming Critical and Improved Martial Arts. Also note that you could drop Precision for Stunning Blow if that is more to your liking. Precision is really just for boss fights where fortification becomes an issue. I don't see any problems with hitting trash on this character.

Twists of fate:
I'm not sure what exactly would be best for this, but I am thinking priorities would be A Dance of Flowers (GoF) for +1.5[W], Primal Scream (FotW) for +5 strength and con, and Tunnel Vision (FotW) for 3d8 damage per swing.

Stat breakdowns:
48 strength = 20 base + 3 tome + 6 levels + 4 heroic enhancements +2 destiny + 7 item + 5 primal scream + 1 exceptional. There are many ways to increase this further, depending on the gear you have available. Not sure what the max is, but it is probably close to 60. But 48 is sufficient to make my point, I think.

32 constitution = 14 base + 3 tome + 3 stance + 5 primal scream + 7 item.

30 wisdom = 15 base + 3 tome + 2 enhancement + 7 item + 3 exceptional.

These are the only three that matter, so that's all you're getting.


Random attempt at determining critical max: AKA, the fun stuff. (Note: highly theoretical and back-of-the-envelope type calculations. I reiterate - this is just for fun. Please do not take overly seriously.)
+x[W] = 1 base +1.5 from 12 monk levels + 1 past life +1 Improved Martial Arts + 1.5 Dance of Flowers twist + 0.5 improved power attack +1 level 20 wraps = 7.5[W].

Base damage = 7.5[1d6] + 19 strength mod + 7 power attack + 1 unarmed mastery + 1 monk past life + 2 ship + 2 weapon specialization = 58.25 average.

Seeker = +2 unarmed mastery + 6 Critical Damage (LD destiny) + 6 Epic RotS = 14 added to criticals.

(58.25 + 14)*5 = 361 approximate average critical damage with power attack active.

Add in a helpless foe with the (hopefully eventually functional) Combat Brute for 2 X 50% increase = 100% extra damage and that should give 722 base damage critical.

If we want to really push this as far as it can go, we can further add in a big stack of Masters Blitz (250% damage), Damage Boost 2 (25% not sure of this is additive for 275% or multiplicative for 312.5%, I assume additive below), max stack of Advancing Blows (+5 damage and to-hit), and a Lay Waste attack (+5[W] and +1 critical multiplier), and then just stand way back...

My calculations come up with a maximum critical damage on a helpless foe of (drum roll please) 2650 damage... per hand!