A blackguard demon summoner? I have just the build for you. (And yes... this was before I decided that NPCs don't need to take Leadership. I wasn't sure if this was an NPC or PC when I first built it, actually.)
He was tweaked with a few house rules, but should be simple to convert back to standard rules. This build is old, and hence there is a ton of new material that could be added to greatly benefit it, I'm sure. I was also using an older (and overpowered) version of Summon Undead. So he shouldn't be summoning any cloud giant skeletons... He could have animated them before the fight, though.
That's quite a nasty build as written. Substitute some Abjurant Champion and Jade Phoenix Mage (Arcane Wrath is much better than Arcane Strike) and it's a monster. I think I likes...
EDIT: Okay, I think I have it figured out. It's pretty much your build, but with a few substitutes.
Warblade 1 / X-Paladin 1 / Blackguard 10 / Nar Demonbinder 1 / Jade Phoenix Mage 5
Feats: Education, Power Attack, Cleave, Improved Sunder, Iron Will, Spell Focus (Conjuration) Southern Magician, Divine Might
This gives Arcane Wrath (+4 attack, +1d10 damage per spell level expended), Initiator Level 12th, 5th level Nar Demonbinder casting, 10th level Blackguard casting, 5 maneuvers known and 4 maneuvers readied. Not to mention a 17 BAB.
So, using an Unholy Chaotic Humanbane Greatsword +2, 26 Strength, 26 Charisma, Smite Good (+8 attack, +10 damage), Divine Might (+8 damage), Arcane Wrath (+28 attack, 7d10 damage) and Power Attack (-17 attack, +34 damage) = +29 attack, 2d6+7d10+60 (avg. 105 dmg.) plus 2d6 Unholy (7 dmg.), 2d6 Chaotic (7 more), 2d6 if human (7 more) and 3d6 if flatfooted (10.5 more). That's 136.5 average if all the conditions are met. Not too shabby for an 18th level melee combatant. I could probably throw in some extra spell conditions for good measure.