World Wonders appears to be 50
New Natural Wonder appears to be 40
Connect resource appears to be 40
Roads appear to be 40
Most Cultural / Religion points / techs appears to be 40
Bankrupt appears to be 20 (on top of what the gold is itself giving)
Clearing barb camp appears to be 50
Denounce appears to be 50
Bully another city state appears to be 40
Great Project for X turns is built into the gold; and unlike the others, if you give money during it, the quest still continues.