What do the plates in Pokemon Diamond and Pearl say?

Answer 1

They reveal the story of Arceus if you put them all together:

"The Original One breathed alone before the universe came." (Sky and Stone plates)

"Two beings of time and space set free from the Original One." (Earth and Spooky plates)

"Three beings were born to bind time and space." (Zap and Toxic plates)

"Two make matter, and three make spirit, shaping the world." (Dread and Iron plates)

"When the Universe was created, its shards became this Plate." (Mind and Splash plates)

"The power of defeated giants infuses this Plate." (Fist and Meadow plates)

"The powers of Plates are shared among Pokemon." (Draco and Flame plates)

"The rightful bearer of a Plate draws from the Plate it holds." (Icicle and Insect plates)

Source: http://www.gamespot.com/ds/rpg/pokemonpearl/show_msgs.php?topic_id=m-1-44334662&pid=925602