Block and Item Displays

•Block Display
/summon MinecartRideable ~0 ~-2 ~0 {CustomDisplayTile:1,DisplayTile:<ID here>,DisplayOffset:45}

•Item Display <No need to change anything except the coords.>
/summon MinecartRideable ~ ~-4 ~ {CustomDisplayTile:1,DisplayTile:49,DisplayOffset:42,Riding:{id:MinecartRideable,CustomDisplayTile:1,DisplayTile:49,DisplayOffset:48,Riding:{id:MinecartRideable,CustomDisplayTile:1,DisplayTile:116,DisplayOffset:63}}}

•Floating Item
/summon Item ~ ~2 ~-1 {Item:{id:373,Damage:8193,Count:0}}