In order, major differences only..
AK-47. The very first AK-47 was stamped, but was replaced by the 'type II' and 'type III' milled receiver. Fires 7.62x39mm. The type I was around from about '49 to '51, the milled versions lasted until '59 or so.
AKS-47. Underfolding stock.
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AKM. Modernized version of the AK-47. Still fires 7.62x39, but uses a new stamped receiver. Also had a different bayonet and lug location. Used from '59 to '74 give or take.
AKMS. Modernized AK with underfolding stock.
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AK-74. New round, 5.45x39, and still uses a stamped receiver. Also introduced a new muzzle brake which is one of the best ever used for reducing muzzle climb.
AKS-74. 74 with a steel triangle folding stock.
AKS-74U. Shortened 74 with a triangle folding stock.
AK-74M. Modernized version of the AK-74. Polymer folding stock becomes standard, still uses a stamped receiver. Current standard rifle of the russian military.
Edit: Should have just linked to this
http://www.gunsnet.net/forums/showthread.php?t=228681