Palenque (Temple of the Inscriptions: tomb of Pakal)
Uxmal, view from the top of the Great Pyramid towards the 'nunnery'
Chichen Itza: sacrifice-stone in the Temple of the Warriors
Tulum: watch-tower on the northern sea front
Tulum is the size of a big British site - same sort of area as Fountains Abbey, no individual building that impressive. But Uxmal and Chichen Itza are both bigger and more filled with buildings than the Forum in Rome; Palenque is even more impressive because most of the site, including the biggest pyramid, is still embedded in jungle.