Chosen of Evil is also pretty nice if you are playing a character with a lot of Vile feats; as an immediate action, gain +[# of Vile feats] as a bonus to an attack roll, AC, or a save.
Of the feats that require it,
Enemy of Good is kinda nice (+2 to the save DC of any spell or SLA you use against a creature with the Good subtype or who radiates an aura of Good.).
Slave to Evil minimizes damage from Evil spells, and you gain a bonus based off the intensity of the current Elder Evil sign (which come to +2 to saves, +1 to attack and damage, SR 11 + Half Level, and the Impeded Magic trait in an aura 30' around you... all of the above only function against Divine spells or Spellcasters.)
Finally,
Master's Will is just silly; as an immediate action, beseech your Elder Evil master for aid. Then roll a d20; if you get an odd result, you get a
+8 untyped bonus on one attack, save, or skill check you make in the next round. If you roll even, you take damage equal to your HD.
All of the above are from Elder Evils, which had some pretty good feats.
I mean, who could say no to
Evil's Blessing? As a Standard action, get a profane bonus to all saves equal to your Charisma modifier for 5 rounds; if you deal damage to a creature with the Good subtype or who radiates an aura of good, the bonus is
doubled for that round. If I was going Paladin hunting, I'd take this feat in a heart-beat.
Apostate gives you a +[1/2 ECL] profane bonus to all saves against Divine spells; however, you can't voluntarily fail a save against Divine spells, and taking the feat breaks the Code of Conduct of any Divine Spellcaster who has one, regardless of alignment.
Abominable Form: Yes, I want the feat that makes everyone with less HD than me have to roll a DC 15 +
2 * The number of Deformity feats I have or be Shaken for Con mod rounds. That doesn't have any limits on how often they have to make the save. Or any limits against stacking. In Elder Evils, there are 7 Deformity feats (strangely enough, the Willing Deformity feats in HoH don't count, because they lack the descriptor; I'd personally allow them to count, but that's just me), for a total possible save DC of 29. Yowch.
Not that the other Deformity feats are necessarily bad either:
Deformity (Eyes): Lets you see Invisible for 1 minute each day.
Deformity (Face): +2 to two skills. This one isn't too good, except for the implicit +2 to save DCs for Abominable form.
Deformity (Gaunt): Makes you into an Elf! More seriously, it gives you +2 Dex and -2 Con. This can be pretty good if you want the extra Dex.
Deformity (Madness): Awesome! It gives you a permanent -4 to your Wisdom score in exchange for
immunity to all Mind-Affecting effects. As an immediate action 1/minutes, add half your character level to a single Will save.
Reflexive Psychosis: Immediate action to get DR 5/- for 1 round, you are Confused for that round.
Deformity (Parasite): As an immediate action, negate a disease or poison affecting you; the next round you only get a Standard action or a Move action, not both.
Hellsworn is pretty niche; however, the Brimstone Caress option is pretty much worth it (constant +1 to the CL of Evil spells and SLAs? 1/Encounter +1 save DC and Corrupt Spell? I'd take it.)