Yes, muslims believe in Angels. Beliving in angels is an integral part of the Islamic Faith. We cannot see them except when we pass away from this world. They were created from a pure shining light and they are of an exhaulted nature and are very beautiful, theya are very huge so much so that the human mind cannot comprehend it. Yes, they serve god and no they do not have any free will. They can only do what god commands them to do.
Their duties are numerous. Some carry the Throne of Almighty god, one is an angel of death which has many workers under it. Some are the gate keepers of Hell and some are the keepers of Paradise. Some angels are appointed individually to record the good deeds and bad deeds of every human being. They have numerous other things that they do.
You will find a detailed view of Angels in Islam in the following thread:
http://www.islamicboard.com/aqeedah/...ml#post1147594