There are some die-hard Maya-philes that want to see all the sites on the so-called Puuc route or Ruta Puuc en español and these generally comprise Kabah, Sayil, Xlapak and Labna, in that order as you are heading out from Uxmal.
There is also Sabacche, which has ruins and a small regional animal preserve, including an ocelot what is friendly and will let you join it in its cage (enter at your own risk) and a really interesting feature that showcases the air currents blowing around in the caves beneath your feet. Opening times there are sporadic so it's not always a sure thing.
If you are really determined, you can also visit the LolTun caves, which kind of make up the end of the route and take you into citrus growing country. Very scenic and photogenic around there, with lots of fruit trees from mangos to oranges to limes and bananas, due to the excellent kankab or red soil.
A day out here, including Uxmal and LolTun, can easily be a 10 to 12 hour day, depending on how interested you are and how much time is spent at each site.
Here are a few shots of the ruins of Kabah, Sayil, Xlapak and Labna, in that order.
Kabah (above) is known for it's long facade of Chaac sculptures covering one entire wall and it's beautiful arch, leading to a sacbe that once went all the way to Uxmal
Sayil (above) is stunning
Xlapak (above) has one pretty building that has been restored and several mounds. There is so little here in terms of restored or reconstructed buildings that the site has no entry fee
Labna (above) has probably the most beautiful Mayan arch in all of the Puuc. It would be fantastic if the INAH could restore the small square around it