1. A marble falling from an 100 hundred story skyscraper window 2. A falling bus sign 3. Donkeys (donkeys kill more people every year than plane crashes)
Three most dangerous weapons, it really depends on how you look at it. Power of Public Opinion/Media is a powerful tool and possibly a weapon, public opinion forced a US pullout of Vietnam, thanks in part to the Tet offensive which the US technically won. The same power has been used as propoganda, such as in Nazi Germany and in the Soviet Union to turn the Soviet people against the Nazis when they invaded. Nuclear weaponary is another powerful weapon, capable of wiping out entire cities and spewing radiation into the air, even knocking out entire national powergirds. However the weapon has only ever been used twice. Chemical and biological weapons are also highly dangerous, they can't be seen or easily detected but can kill hundreds easily. Disease itself is highly dangerous even when not used as a weapon, look at the Black Plauge and Influenza in 1918. The AK-47 on the otherhand, while only a simple assault rifle, is a very simple and easily available assault rifle that has killed more people then most, if not all, other modern weapons. And let's face it, this old piece of Soviet firepower isn't going anywhere, especially with newer additions such as the AK-74, AK-101, AK-103, and so on, it and it's variations will still be shooting out it's lethal lead long after we're all dust. Not bad for a cheap Soviet gun. But, look at the knife. One of mankind's oldest weapons, it still kills today. If you counted up every life claimed by the all the different variations of knives throughout human history, the number would put the Holocaust to shame. It would probably even rival China and India's current population.
So, here's my list: 3. Control of public opinion/Media 2. AK-47 assault rifle and it's variants. 1. The Knife.