First enable Debug Mode then have either a unit or a city selected and push the following keys.

Code	Effect
(City) Shift +"+"	Add 1 to city population
(City) Ctrl + "+"	Add 10 to city culture
Highlight a city. [Ctrl] + [Alt] + Left Mouse Button	City editor
Shift + [	Decrease highlighted unit's strength by 0.2
Ctrl + D	Display debug menu
(City) "+"	Immediately complete whatever the city is producing
Ctrl + 4	Increase gold by 1000
Ctrl + Plus	Increase highlighted city's culture by 10
Shift + Plus	Increase highlighted city's population by 1
Shift + ]	Increase highlighted unit's strength by 0.2
Ctrl + Shift + Left Mouse Button	Insert unit/city
Plus	Instant production completion for highlighted city
Ctrl + Plus	Level up highlighted unit
Shift + T	Pops up a dialogue to change a certain nations gold and change the era
(Unit) Ctrl + "+"	Unit level up
Ctrl + W	World editor