The dates given by the archaeologists (not the new-age-is-coming folks) are correct and take into account various reworkings of the calendar. December 12 is correct.

But there's no significance to the calendar ending... or, rather, no more significance than my 2006 Dilbert calendar coming to an end. The "new world age" writers tend to "channel" their information and know very little about the society and its beliefs, though they may have taken a peek at the Popul Vuh and rather managled the information in there.

The "new age" people believe that the Mayans believed a new cosmic order would come about on that date. The living Maya people have no such belief, and they are largely unaware that 12/12/12 has any special significance or will bring a "new age of enlightenment." To most of them, it's "13 days before Christmas, 6 years from now"
[caliber.ucpress.net]

The associated "alignment of the Earth with the center of the galaxy" is also not correct. We are always aligned with it... what will change is that the wobble of the Earth (the precession) will have moved in its cycle so that the dark rift in the milky way coincides with the vernal equinox.