Scary Scales, the Dragonborn Hexblade.
Race: Dragonborn with the breath weapon, base race: Any without a Cha penalty. Cha bonuses are nice too.
1: Hexblade, Intimidating Strike*
2: Hexblade
3: Hexblade, Entangling Exhalation
4: Hexblade, Dark Companion
Notes: Max out Intimidate. Use your breath weapon to keep the enemy entangled. Then, using a reach weapon and intimidating strike to make the BBEG shaken, then curse them when their saves are the lowest. With your dark companion in the mix this should be relatively easy. In two or three rounds you can leave your foe with -6 to attacks, -6 to saves, -4 to checks, -2 to damage and AC, and -4 dex. And you can do that without expending any resources, other than the 1/day curse, but frankly that's the least of your debuffs.
Also, unlike a lot of other debuffers built around fear, this guy remains flexible in a fight against undead and fear/mind-effect. Entanglement works against just about anything (remember that Dragonborn can cherry-pick the energy effect with each blast, and there is no save against the entangling so long as the target takes some damage from the breath attack. Dark Companion also works against 'any enemy.'
I like intimidating Strike because of its long duration - Making a foe shaken for the encounter is nice. However, Daunting presence is an acceptable alternative if you don't mind the shorter duration and want to stay out of melee.
Sources needed:
[spoiler]
Complete warrior for Hexblade.
Races of the Dragon for Dragonborn and Entangling Exhalation
PHII for Dark Companion alternate class feature and Intimidating Strike.[/spoiler]