In "The Rime of the Ancyent Marinere", the Marinere encounters many troubles, but some good luck too. After the Marinere admitted to shooting the Albatross with his crossbow, the crew is very angry. Then they realize the Albatross was not responsible for the wind behind their sails (but for the fog), and they praise the Marinere. But when the ship sails into the evils of the sea the crew then hangs the dead Albatross around the Marinere's neck, he is blamed once again. "Instead of the Cross the Albatross About my neck was hung". I see the dead Albatross as a symbol of the wrong-doing ("evils") of the Marinere and the devil that resides in him. Not only is it clearly stated as an antonym to the Cross (his exclusion from Christ), the Marinere and the crew encounter evils (Death, Life-in-Death, slimy sea creatures) on their continued voyage. In addition, "I look'd to Heaven, and try'd to pray; but or even a prayer had gusht, A wicked whisper came and made My heart as dry as dust". The Marinere tried to pray to Heaven but was unable to, and during the seven days and seven nights his cursed crew lay dead around him he was not able to die, be saved and go to Heaven. I feel the Albatross was what was holding him back from his prayer and salvation. When he had unknowingly blessed the sea creatures, he found himself able to pray again and the Albatross had fallen off his neck. It was apparent in many different stanzas that the Albatross was the cause of the Marinere's unrest.
Halfway through reading this poem I searched some images to help give me a mental picture while reading, the above image is one of a few I found.
Photo taken from: http://www.martinezbeavers.org/wordpress/wp-content/uploads/2008/10/albatross.jpg