Ameraucana: bred from South American birds carrying the blue egg gene, mostly purified out of Easter Egger stock (which is why hatcheries try to say their EEs are Ameraucans, they somewhat resemble each other). Features include: Slate colored legs, pea comb, lays blue or green eggs, has a muff and beard, comes in the following colors: Blue, Blue Wheaten, Black, Brown Red, Buff, Silver, Wheaten, and White. CANNOT come in any other colors.
Araucana: Developed in Chile and refined in the US; not bred from EE stock. Features include: Lack of tail (rumpless, although tailed birds may be used in breeding programs, just not shown), pea comb, tufts of feathers protruding from cheeks and sweeping back (no muff or beard), variable leg color, standard size comes in black, white, black breasted red, silver duckwing, and gold duckwing.
Easter Egger: Not a true breed, and thus type is not regulated and can vary wildly. Bred by US hatcheries in an effort to sell colored eggs at higher markup, most likely bred from South American birds. Ideal EE traits: Muff and beard, pea comb, willow colored legs, blue to green eggs. Can come in any coloration. Can have only one or two of the above listed features, and still be called an EE (yes this means they could lay you a brown egg).