As far as real AK-47's go (the real NFA Title 2/Class III restricted kind)--an "AK-47" is the original, milled receiver, selective-fire version. The "AKM" or "AKM-47" is the more familiar variant, with the stamped receiver. The AK-74 is the 5.45x39mm derivative.
As far as non-automatic, civilian AK lookalikes (guys, correct me if I get any of these wrong):
SAR-1, Romanian AKM lookalike in 7.62x39mm
SAR-2, Romanian AKM lookalike in 5.45x39mm
SAR-3, Romanian AKM lookalike in 5.56x45mm/.223 Remington
WASR-xx, any of a series of Romanian AKM lookalikes that came after the SAR's stopped being made/imported.
Saiga - Russian sporter-style rifles built on civilian AKM type receivers; some have straight Mauser-style stocks, and some have been converted in the U.S. to regular AKM-style configuration, with a separate pistol grip.
Vepr - Russian rifle built on a thick RPK-style stamped receiver (can be identified by the slant-cut receiver rear and other cosmetic differences)
MAK-90, NHM-90 - Chinese AKM lookalikes; some were in AKM-style configuration and some had thumbhole stocks; importation ceased in 1990's.
There are also some Polish and Hungarian AKM lookalikes that I can't recall the names of at the moment.