Empath Aura - Increases diplomatic bonuses and relation gains from envoys in gravity well (faster for both parties).
Low Gravity Simulators - Capital ships start with more experience.
Dense Metal Alloys - Increases structures' armor rating.
Cryogenic Chambers - Planetary bombardment has reduced effect on population.
Repulsor Field - Enemy movement towards planet in the gravity well is significantly reduced.
Propaganda Satellites - Grants a boost to planet allegiance and friendly culture bonuses.
Symbiotic Lifeforms - Doubles population gains and losses.
Historical Archives - Reduces planet upgrade costs.
Quantum Encryption Protocols - Jams PSIDAR readings (jumps from this planet are invisible).
Holy Memorials - Reduced cost for civilian labs; increased cost for military labs.
Probably not all viable but this is really fun.