Remove Gold Reward for Champion Kills and Turrets
The snowball problems in the game have been discussed a lot on these forums. The analogy is made, "what if in football when you scored a touchdown you got to put an extra player on the field?" That would obviously lead to blowouts in 90% of football games, and that's exactly what we have in LoL.
The answer is very obvious, but it is so different from what you're used to that most of you will reject it out of hand. Simply remove any gold reward for champion kills or turrets destroyed. The point of killing a champ is to take him off the map and give you an advantage in taking objectives. The point of taking objectives is to get to the nexus and win the game. Getting gold is a double bonus analogous to the football team getting an extra player. Just get rid of it.