Captain America's Shield

Captain America's Shield is a primary defensive and offensive piece of equipment for battle. His shield is made out of Vibranium.

Captain America: The First Avenger
Captain America's shield was a shield made form the only available vibranium that the U.S. Military had. Howard Stark gave the shield to Captain America to protect himself from gunfire. Captain America used the shield in all of the attacks on enemy factories and other missions. He had the shield with him when he crashed at the pole. About seventy year later, S.H.I.E.L.D. agents had stumbled across the crashsite of Captain America's plane. He was found alive, and he and the shield were taken to their proper place.

Iron Man
Tony Stark kept a prototype of the shield in his lab.

Iron Man 2
The shield prototype was found by Agent Coulson in Stark's lab. Stark claimed that the shield was just what he was looking for. He then set it under an electrical wire in order to make it higher.

The Avengers
When Captain America was called upon to join The Avengers, he again relied on the shield for as his primary weapon. He saved a civilian in Germany by blocking a shot fired by Loki. The shield also saved the captain's life when he it protected him from an attack from a confused Thor, while everything else around them got destroyed. They were later able to take Loki into custody.

Captain America relied on his shield once again during the Chitauri attack on Manhattan. The shield was being repeatedly flung at Chitauri warriors as it either disarmed them or knocked them out. The shield was not seen again after the battle was over.

Trivia

 * The shield was originally supposed to be made out of a mix between vibranium (for absorbing vibrations) and adamantium (for its near in destructibility), as in the comics. However, since 20th Century Fox holds the rights to the X-Men, this was changed to be completely made out of vibranium.
 * In Iron Man and Iron Man 2 a prototype of the shield can be seen. It is possible that it is the shield seen in The Avengers, just not compleated.