What's a good prestige class for blackguards?

[CaDzilla]

Even though they're already a PrC, what are some good PrCs they can enter if you take 5 levels?

[atemu1234]

Well, there's always blackguard...
Maybe Abjurant Champion?

[A_S]

Well, Bone Knight also benefits from having ex-Paladin levels hanging around, so you can get nifty stuff like 2x your Cha bonus to all saves. The Aura of Despair also works well with stuff that targets saving throws, so fear-based builds can be pretty strong.

Really, though, Blackguard just isn't that good.

[Waker]

Shadowbane Inquisitor can be decent, especially if taken before going into Blackguard, since the class counts as Paladin for determining bonus abilities and you get Improved Sunder as a bonus feat.
Ordained Champion has some potential.
Did you have any specific idea for a character other than, "Blackguard"?

[Rhaegar14]

Well, not a PrC, but Crusader of whichever Evil deity has a lot of the same themes and does receive some benefit from the Blackguard levels (namely, an increase in initiator level).

[WeaselGuy]

I'm playing a Paladin of Tyranny/Feat Rogue/Blackguard right now, who's about to PrC into Warrior of Darkness from BoVD... gives it even more that "Hey look at all my evilness!" feel...

[Fax Celestis]

Ruby Knight Vindicator, with an alignment relaxation? Ghost-Faced Killer?

[Divide by Zero]

Not a prestige class, but 4 levels of Hexblade with the Dark Companion ACF gives you even more save penalties to throw around.

[Madhava]

Prestige classes only? Meaning, you absolutely aren't considering base classes?

Hm. Tenebrous Apostate, maybe. Bind Focalor for extra-debuffy-goodness.

Occult Slayer is not terrible, but this would tie up even more of your feats.

Or maybe War Mind; ten levels if your wisdom is high-ish. Five levels if it's not.

[daremetoidareyo]

Divine oracle (complete divine) is interesting, max out those blackguard spells.

Spymaster is fluff rich.

I also like shadow blade (TOM) Stacking some of those sweet blackguard buffs on top of the extra sneak attack damage is nice. If he starts as a swordsage, before turning blackguard, some shadow stances and maneuvers would be sweet! Particularly if you go with the unarmed focus as a swordsage, and deliver touch spells as part of your attack.

[gorfnab]

Ex-Paladin 1/ Blackguard 10/ Nar Demonbinder 7/ Crusader 2
Duskblade 2/ Ex-Paladin 1/ Blackguard 10/ Nar Demonbinder 2/ Abjurant Champion 5
Ranger 3/ Ex-Paladin 1/ Blackguard 10/ Horizon Walker 6 - Core Only

[deuxhero]

Paladin of Tyranny 4/Hexblade 4 (Dark Companion)/Blackguard 7/Entropomancer 5 was given in the first Iron Chef here and still a nice ally to have around because it crushes enemy saves just by standing there (and he can do more).