This must have been raised before, but let's get all the ideas (especially the new ones) down here.
My suggestions
Theatre:
Cost- low
Upkeep- 1
Effect- +1 luxury for each 10 gold produced
Requires- Literacy
Opera House:
Cost- medium
Upkeep- 4
Effect- +1 luxury for each 10 gold produced (cumulative with theatre)
Requires- Steam Engine (or classical music if it gets put in), Theatre
Parks:
Cost- low
Upkeep- 0
Effect- +1 happiness
Requires- Philosophy
Radio Station:
Cost- Medium
Upkeep- 2
Effect- 1/4 all unhappy citizens content
Requires- Radio
Television:
Cost- High
Upkeep- 5(state economies), 2(capitalist systems)
Effect- 1/2 all unhappy citizens are content (includes effect of radio station)
Requires- Miniturisation, Radio station
My suggestions
Theatre:
Cost- low
Upkeep- 1
Effect- +1 luxury for each 10 gold produced
Requires- Literacy
Opera House:
Cost- medium
Upkeep- 4
Effect- +1 luxury for each 10 gold produced (cumulative with theatre)
Requires- Steam Engine (or classical music if it gets put in), Theatre
Parks:
Cost- low
Upkeep- 0
Effect- +1 happiness
Requires- Philosophy
Radio Station:
Cost- Medium
Upkeep- 2
Effect- 1/4 all unhappy citizens content
Requires- Radio
Television:
Cost- High
Upkeep- 5(state economies), 2(capitalist systems)
Effect- 1/2 all unhappy citizens are content (includes effect of radio station)
Requires- Miniturisation, Radio station