Inspired totally by a World of Warcraft Death Knight. ;)
A Paladin, captured and forced to undergo the rite to become a Necrolpotian (as a darstedly punishment!), who is then controlled and forced into evil acts.
Changes allignement and loses thier Paladin-ness. Later breaks control and tries to reestablish his own (and previous) life. Starts to follow the path of the Bone Knight.
Human (Power Attack)
1: Paladin (Extend Spell)
2: Paladin
3: Paladin (Persist Spell)
4: Paladin
5: Bone Knight
6: Bone Knight (DMM: Persist Spell)
7: Bone Knight
8: Bone Knight
9: Bone Knight (Battle Blessing)
10: Bone Knight
11: Bone Knight
12: Bone Knight (Improved Bull Rush)
13: Bone Knight
14: Bone Knight
15: (Shock Trooper)
How would you round this out (No ToB...)? Take a Cleric dip for Domains? Divine Crusader or Ordained Champion?
Would like to fit Improved Toughness in there somewhere.
Don't really need to take Bone Knight all the way, as being Undead I'd already have the immunities Bone Knight offers. Could always leave Paladin at 2, dip Cleric and maybe Fighter (for the extra feats) and enter Bone Knight a level later.
I'd add in some blackgaurd. Thats basically exactly what the prestige class is for. I'd also go 5 levels in paladin for your mount.
If you want to multiclass go into hexblade for a 2 level dip. Grap cha to saves vs spells, and ensure you are never controlled or forced into any acts again.
You don't get the Mount if you go Bone Knight. But you get thier Skeletal Mount at level 2 instead.
Blackguard is nice, but I was aiming for a still Godd (if not Lawful Good) charcater and not an evil one. 
So it does, and it apparently stacks with paladin levels without needing to get 5 levels of paladin first.
Take a look at some hexblade levels then.
They don't stack, so if for example, you only take one Paladin level, you wouldn't ever get Divine Grace. 
Plus the Bone Knight requires Turn Undead and 1st level Divine Spells for entry. You can get those (and the +4 BAB) from 4th Paladin, but if you drop any, you'd need at least a cleric Dip.
Mettle seems nice, but apart form that why Hexblade? The curse seems lackluster. There's the ACF that changes that though. Maybe that's worth it.
Because its cha to saves totally stacks. Different untyped bonuses from different sources. Why wouldn't they?
Really outside that it is lackluster
Ah! Spell Resistence.
Not quite as good as Divine Grace, but if you're utilising CHA anyway.
Mettle might also be worth picking up at 3rd?
Its debatably decent. I mean, nice to have, but you shouldn't be failing saves at that point. Cha to saves X2 + Save bonuses + Actual stats. If you are looking for filler levels go at it, but otherwise I wouldn't bother.
The choice is then;
Paladin 4 (Divine Grace, Lay on Hands, Aura of Courage, Divine Health, Turn Undead)
Or getting into Bone Knight 1 level later and taking;
Paladin 2, Cleric 1, Hexblade 2 (Divine Grace, Lay on Hands, Turn Undead, Domain Access, Curse 1/Day, Arcane Resistance)
The issue here is that you would have to check the wording on;
If your only divine spellcasting ability prior to becoming a bone knight was as a paladin, you continue to advance your paladin spellcasting as normal. In addition, you add the following spells to your spell list, as if they appeared on the paladin's spell list: 1st—bane, deathwatch, doom; 2nd—death knell, desecrate, gentle repose; 3rd—bestow curse.