I was just reading something in another thread about wanting more diplomacy options, which reminded me of the following:

When a friendly faction begs me for help because it's being crushed by a mighty opponent, I sometimes bribe the enemy faction to make peace with my friend. I would like the friendly faction to recognize this gesture in words and/or improved relations. As it is now, I usually receive only insults because I did not provide money or techs on the spot.