I really love the list of common misconceptions wiki page.
Some of my favorites:
Napoleon Bonaparte was not short; rather he was slightly taller than the average Frenchman of his time. After his death in 1821, the French emperor's height was recorded as 5 feet 2 inches in French feet, which is 5 feet 7 inches (1.69 m). Some believe that he was nicknamed le Petit Caporal (The Little Corporal) as a term of affection.
It is commonly claimed that the Great Wall of China is the only human-made object visible from the Moon. This is false. None of the Apollo astronauts reported seeing any specific human-made object from the Moon, and even Earth-orbiting astronauts can barely see it. City lights, however, are easily visible on the night side of Earth from orbit. Shuttle astronaut Jay Apt has been quoted as saying that "the Great Wall is almost invisible from only 180 miles (290 km) up. ISS commander Chris Hadfieldattempted to find it from space, but said that it was "hard as it's narrow and dun-colored."
A duck's quack actually does echo, although the echo may be difficult to hear for humans under some circumstances.
Despite being commonly believed today, people during the Old and Middle English speaking periods never pronounced or spelled "the" as "ye". The confusion derives from the use of the character thorn (þ) in abbreviations of the word "the", which in Middle English text looked similar to a y with a superscript e.
There is no evidence that Vikings wore horns on their helmets. In fact, the image of Vikings wearing horned helmets stems from the scenography of an 1876 production of the Der Ring des Nibelungen opera cycle by Richard Wagner.
Thomas Edison did not invent the light bulb. He did, however, develop the first practical light bulb in 1880 (employing a carbonized bamboo filament), shortly prior to Joseph Swan, who invented an even more efficient bulb in 1881 (which used a cellulose filament).
Christopher Columbus's efforts to obtain support for his voyages were not hampered by a European belief in a flat Earth. Sailors and navigators of the time knew that the Earth was roughly spherical, but (correctly) disagreed with Columbus's estimate of the distance to India, which was approximately one-sixth of the actual distance. If the Americas did not exist, and had Columbus continued to India, he would have run out of supplies before reaching it at the rate he was traveling. Without the ability to determine longitude at sea, he would not have learned that his estimate was an error in time to return. Many of the educated classes believed the Earth was spherical since the works of the Greek philosophers Plato and Aristotle. Eratosthenes made an accurate estimate of the Earth's diameter in approximately 240 BC.
There are tons of them!