Since Zack brough 8 ways to kill good ideas, I thought I'd add two of my own that I see popping up frequently.
Insist on following procedure
People work differently, and those coming up with ideas that they want to try out are usually not good rule-followers. When forced to follow a certain procedure, only because it's company policy or because management want to reduce the risk (which is usually what the procedures are for), the idea will surely not get implemented.
On an interview I was once asked the question "do you have many bad ideas?". I answered that "90% of my ideas are usually bad", to which the interviewer smirked and said "Not more? That's pretty good." This was for a job where the continous creativity of their employees where the very essence of their survival, so the managers assumed that there would be many bad ideas and only a few good ideas. They assumed that time would be wasted on bad ideas, but considered that as part of the trade.
By punishing failures, you send a clear message that risk-taking is not looked kindly upon. Therefore nobody will take any risks; you do not waste time on any bad ideas, but in effect you will not get any of those world-changing good ideas either.