PickUp, an ability that a few Pokémon have, allows for the Pokémon in question to have a 10% chance of finding an item after battle. In RSFRLGCXD, these were a set few items with varying rarities. diamondpearl however brought in the inclusion of different items at different levels. Diamond & Pearl follows this inclusion with their own items. Below are the Pokémon that can learn this Ability. Click them to go to their Pokedex entry

Meowth	Aipom	Teddiursa	Phanpy	Zigzagoon
Linoone	Pachirisu	Ambipom	Munchlax

Now, each Set of Levels have varying items, with some items being rare for the lower levels but common for the higher levels. Hover over the items for their name:

Lv.	Common	Uncommon						V. Unc.	Rare	V. Rare
1 - 10
11 - 20
21 - 30
31 - 40
41 - 50
51 - 60
61 - 70
71 - 80
81 - 90
91 - 100