I'd say Graptopetalum (maybe 'Ghosty') and/or perhaps X Graptoveria or cultivar thereof. But as they said, the looks of them can change as they grow. At least mine do. You can look at them at different times of the year and not think it's the same plant. Sun and shade make a big difference as well. Sometimes the flower can tell the tale and make for an ID. :)
One of the Graptosedums or Sedeverias are also possibilities for the bottom one. There are so many crosses (X) among the succulents due to the fact that they cross so easily.
http://crassulaceae.net/forum/...
