Archaeology of Mexico
As someone who has traveled extensively through Mexico, I'm going to give you the scoop on the ruins from the perspective of a tourist rather than an archaeologist (which I'm not). This is my list of best archaeological sites in Mexico.
Top Archaeologic Sites in Mexico
Teotihuacan (about 25 mi North of Mexico City) is the first on this list because it is the most impressive in terms of scale and restoration. This site is truly huge with the Pyramid of the Sun rivaling the grandeur of the great pyramid of Cheops in Egypt. If the priests had to climb that thing every day, there were no fat priests (stair master + altitude that will kick your butt).
Palenque (usually visited from Villa Hermosa or San Cristobal de las Casas) makes number two on my list for its extremely well preserved structures. This ancient city is (in my opinion) the most beautiful ruin in Mexico.
Monte Alban (Oaxaca City) comes in as third for its extreme difficulty in construction. Located on a mountain overlooking three valleys, the builders sheered off the top of the mountain to flatten it, built it to catch every bit of rain water and store it under the city, and subterranean passageways that went from one temple to the other.
Tulum (south of Playa del Carmen) comes in fourth because of its extreme scenic beauty on a cliff overlooking the Caribbean . . . and the nearby Coba ruins that is still being excavated, but makes a great companion trip while in the area.
Uxmal (from Merida) comes in fifth. These ruins are not as popular as the ruins of Chichen Itza (a tad closer to Cancun) but they are (in my opinion) more impressive.
Chichen Itza then comes in sixth. Though many would argue the point based on archaeological importance, I'm writing about what I saw and what impressed me.
There are tons of other ruins in Mexico and I would whole heartedly recommend that you visit any ruins that are near your destination. The history of a people etched in stone is what gives us some perspective on the culture.
Remember that you will need to pay an entrance fee to get into the major ruins and that you should bring water, sun screen, and a good camera.
Above all, try to learn something about the ruins before you get there. Unless you are planning on hiring a guide, there is a lot you will miss if you aren't looking for it.