I've got a bevy of new feats for your delectation here; more may be added at my whim. Any thoughts?
Empty Soul
Prerequisites: Amoral, ability to cast three necromancy spells of level 2 or higher
Benefit: When the subject of any divination spell, you may make a Charisma check as per Amoral to disguise yourself as undead. By increasing the DC by 5, you may attempt to disguise yourself as mindless undead like a zombie or a skeleton. Spells which also pierce illusions, such as true sight, are not affected.
Picture of Innocence
Prerequisites: Amoral, Bluff or Disguise 8 ranks, Base Will save +5.
Benefit: You get a Will save against any spell, spell-like ability, ower, psi-like ability or supernatural effect that detects alignment. This is in lieu of any similar benefit, if applicable -- i.e. this does not stack with any similar ability -- and the DC is 10 + (half caster level or HD) + caster's Charisma bonus. If the save is made you may masquerade as any alignment you please, including "alignment unknown", or have it give no answer as per the Amoral feat. If the save is failed, you may still reduce the intensity of your aura (as per the table in the Player's Handbook) by one degree. The character detecting your alignment does not know that you get a saving throw regardless of whether you make the save or not.
Additionally, if your alignment is magically disguised (for example, by means of a misdirection spell), you get a Will save with the same DC as above against any attempt to detect that disguise. If you make the save, the disguise is not detected.
Alignment Camouflage
Prerequisites: Amoral, Picture of Innocence, character level 12th.
Benefit: You automatically adopt the alignment of any plane you're on for the purposes of detection, divination, and alignment bonuses/penalties. If the plane has an alignment type, divination spells or effects that do not specifically target you consider you to be something mundane and commonplace to the plane. You receive bonuses commensurate with being a native to the plane, although you are still vulnerable to the non-alignment environmental effects and still technically of the Extraplanar subtype and so can be banished as usual.
Although you cannot fool foreigners, natives to the plane must make a Will save against 10 + your character level to recognize you as non-native. [This is of mixed benefit on, say, the Abyss.] Extended conversation can reveal you as an impostor, but you also receive a +10 bonus to all Bluff, Disguise and Diplomacy checks with any native to the plane until the native makes the relevant opposed check. Once the native has seen through your disguise, you may never fool them in this way again.
Home Away From Home
Prerequisites: Must have made kip in the target plane for over a year.
Benefit: Choose a plane that you have made kip on for over a year. When you are subjected to dismissal, banishment or any similar effect, you may opt to be banished back to this plane instead of your home plane. If you are being banished from your "home away from home", you must return to your plane of origin as normal.
Special: For the purposes of this feat, Sigil counts as part of the Outlands. You cannot, however, specify that you will be banished into Sigil proper.
Iron Gullet
Prerequisites: Fortitude Save +5, Con 11
Benefits: You may consume any foodstuff suitable for any being of your type without ill effect. Additionally, you gain a +4 saving throw bonus against ingested poisons, and a +2 saving throw bonus against nausea or scent-related effects.
Linguist
Prerequisites: Speak at least five languages total, speak at least one outsider language (e.g. Modron, Celestial, but not Planar Trade), speak at least one mortal language (e.g. Elven, Orc), speak at least one elemental language (e.g. Terran, Ignan).
Benefits: You have mastered the art of communication. First, Speak Languages becomes a class skill for you. Second, provided you have conversed with a creature of the same type as your interlocutor, you may communicate without difficulty. This means you receive no penalties on Diplomacy checks, Bluff checks (including combat feints against intelligent beings) and Intimidate checks regardless of any language, racial or cultural barrier. Finally, you receive +1 to Diplomacy, Bluff and Intimidate to any interaction with beings whose language you are fluent in.
Attraction of Opposites
Prerequisite: Control 5 ranks, any neutral alignment.
Benefit: Three times per day you may, as a move action, cause a character within 50' of you to take a 5' step towards another character of opposite alignment on either the moral or ethical axis. This other character must be within 50' of the targeted character and there must be a legal 5' step that can bring them closer. If there are multiple possible opposing characters, you may choose which character they are attracted to.
The 5' step is considered a swift action and does not provoke attacks of opportunity. This is a supernatural effect, and the targeted character receives a Will save at DC 15 + your Charisma modifier if they wish to resist. For the purposes of this feat, neutral is not considered opposed to anything.
Repulsion of Opposites
Prerequisite: Attraction of Opposites, BAB +5, any neutral alignment.
Benefit: Three times per day you may exert your will to cause opposed alignments to attack each other without mercy. Characters of ethically opposed alignments attack each other with a +2 circumstance bonus; characters of morally opposed alignments gain a +2 circumstance bonus to damage. This is a supernatural effect that affects all characters within 30' of you. For the purposes of this feat, neutral is considered opposed to anything not neutral.
Balance of Opposites
Prerequisite: Attraction of Opposites, Repulsion of Opposites, Fortitude Save +8, Will Save +8, character level 12th, any neutral alignment.
Benefit: Once per day, you may invoke a field of neutrality that weakens all those who are not in balance. Any character whose alignment does not contain some component of neutrality takes a -2 penalty to all rolls: attacks, damage, saves, everything. Any character who alignment contains exactly one component of neutrality takes a -1 penalty to all rolls. Any character who is true neutral gets a +1 circumstance bonus on all rolls. This is a supernatural effect that affects all characters within 50' of you, as well as all effects that are targeted or centered within that radius, and lasts for 3+Charisma modifer rounds (minimum 1).
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Ah, there's nothing quite like a fresh batch of Planescape-related feats to dissect...
Empty Soul: Do you get the bonus even if you're not aware of the divination attempt? Also, you say "any divination spell", and then exclude those that "pierce illusions"; what does that leave, detect undead? Generally unclear.
Picture of Innocence: Again, is the character aware of an "Detect Alignment" attempt? If not, is the "mask" randomly determined? Also, the name of the feat suggests an evil-aligned creature disgusing as a good-aligned one, which is not always the case.
Alignment Camouflage: The alignment part is already covered by the prerequisite feats.
Iron Gullet: Primary benefit unclear. Define "foodstuff", "suitable", and "ill effect". The second sentence seems to suggest that none of the previous three terms includes poisonous substances?
Linguist: Looks like a d20 Modern talent (which is also called Linguist, IIRC). Underpowered. Consider giving a permanent tongues effect (Su) instead.
Attraction/Repulsion of Opposites: Do you need to be aware of the alignments of targets for the effect to work? If yes, then the use of the feat is severely limited. If no, the feat suddenly provides a weird and complicated "Detect Alignment" effect (which was not the idea, IIUC).
Balance of Opposites: Is the effect detectable in some way? If yes ... (see above). Also, a flat numerical bonus is typically applied only to task resolution rolls (attacks, saves, skill checks, and ability checks; all d20 rolls, in other words), and not to damage rolls, various percentage rolls, etc. This unwritten rule serves to quantify the usefulness of a bonus.