This list is actuallly complete
Credit given whenever I know the source of an image - if you spot one you recognize, let me know the source!
/- Buildings -/
War Meeting Room => thenounproject.com/icon/card-game-23936/ The Divine Knowledge => Eye of Rayna Yang on the Noun Project Homestead => Courtyard of Loris on the Noun Project
/- Improvements -/
Data Encryption Analysis Center => see DeCiv Redux Hacking Site credits