Europa Universalis III Cheats & Tips

While ingame, hit § (the key under ESC for some people), ALT+21 on the numpad to access the console.
You can now use the following codes, has to be case sensitive:

colonist Colonists added!
diplomat Diplomats added!
fow off Fog Of War turned off.
fow on Fog Of War turned on
prestige Glory to us!
merchant Merchants added!
missionary Missionaries added!
die native Natives are now attacking
cash Now we have cash
pirate Pirates now roam
discover Province type discovered.
undiscover Province type undiscovered.
revolt Revolt created.
spy Spies added!
stability Stability for the People!

Type "invest" plus "type of tech" plus "amount of cash". I.e. "invest land_tech 20000" = $20,000 invested in land technology:

advisor_arrived_tech = (insert number) of cash invested in advisory
land_tech = (insert number) of cash invested in and technology
country_morale_tech = (insert number) of cash invested in country morale
current_tech = (insert number) of cash invested in curren technology
government_tech = (insert number) of cash invested in government technology
ledger_goverment_tech = (insert number) of cash invested in ledger government
ledger_naval_tech = (insert number) of cash invested in ledger naval
ledger_production_tech = (insert number) of cash invested in ledger production
naval_tech = (insert number) of cash invested in naval technology
production_tech = (insert number) of cash invested in production technology
trade_tech = (insert number) of cash invested in trade technology