I could probably expand their spell choices some, but their CL will never be superb.
I played around with some different ideas and this seemed to sound about right to me:
I'll give it some more thought and maybe put this one on my "to do" list. I have a lot of dev work piled up in general, so it probably won't be done any time soon.Poison Use: Blackguards are skilled in the use of poison and never risk accidentally poisoning themselves when applying poison to a blade.
Turn Undead (Su): At 1st level, the blackguard gains the ability to rebuke or destroy undead as would an cleric of two levels lower.
Spellcasting: Beginning at 2nd level, Blackguards get a spellbook and are capable of casting first tier spells. At 4th level they become capable of second tier spells. At 6th level they become capable of casting third tier spells. At 8th level they become capable of casting fourth tier spells.
Smite Enemy (Su): At 2nd level, the blackguard gains the ability to smite any target he deems an enemy. For the duration of one round, he adds his Charisma modifier to his attack roll, and his Blackguard levels to the damage roll. This ability has a cooldown of five minutes, which shortens to two minutes at 5th level, and one minute at 10th level.
Dark Blessing (Su): Beginning at second level, a blackguard applies his Charisma modifier (if positive) as a bonus on all saving throws. This bonus is capped at the user's number of Blackguard levels.
Aura of Despair (Su): Beginning at third level, the blackguard radiates a malign aura that causes enemies within 10 feet of him to take a -2 penalty on all saving throws.
Divine Might (Su): At 4th level, the blackguard gains the Divine Might feat for free, regardless of whether he meets the requirements or not.
Sneak Attack (Ex): This ability, gained at fourth level, is like the rogue ability of the same name. The extra damage increases by +1d6 every third level beyond 4th (7th and 10th). If a blackguard gets a sneak attack bonus from another source the bonuses on damage stack.
Summon Fiend (Su): At 5th level, the Blackguard can summon a hellfire hound (which grows in strength once more at level 10).
Divine Shield (Su): At 6th level, the blackguard gains the Divine Shield feat for free, regardless of whether he meets the requirements or not.
Blood Bond (Su): At 8th level, if the blackguard is harmed in combat, the blackguard's Aura of Despair is modified to also give a +2 bonus to attack rolls and saving throws to all of the blackguard's allies within the aura's area of effect. This effect lasts for three rounds after the blackguard is harmed. Repeated injuries renew the effect, but it does not stack with itself.
Profane Strength (Su): At 10th level, once per day, the blackguard may call upon his patron to grant him a +8 bonus to Strength for 10 minutes.