The following items can be found at the indicated locations.

Big Root: Found in Pinwheel Forest or 5% chance from a wild Lileep or Cradily. This item increases the HP that results from successful Energy draining moves (for example, Leech Seed).
Black Sludge: Has a 5% chance from a wild Trubbish, Croagunk, or Toxicroak or 50% chance from a wild Garbodor. This item restores 1/16th of a Poison-type Pokemon's HP every turn. It damages other types when held.
Experience Share: Given to you by the CEO/Janitor of the Battle Company on the Floor 55 in Castelia City.
Leftovers: Found in a garbage can under the Village Bridge between Route 11 and Route 12. The Dousing Machine must be used to find it. This item restores 1/16th of a Pokemon's health every turn.
Lucky Egg: Given to you by Professor Juniper when you arrive at Chargestone Cave on Route 6. This item gives extra experience points to the Pokemon holding it in any battle it participates in.
Macho Brace: Found in Nimbasa City, from a man standing at the eastern gate. This item will doubles the EV points the Pokemon gets in battle but will halves its speed stat.
Scope Lens: Found on Floor 47 in the Battle Company in Castelia City. This item boosts a Pokemon's critical hit ratio.
Power Hold items: Purchased at the Battle Subway.
Power Weight: +4 HP EV points after every battle, 50% speed stat.
Power Bracer: +4 Attack EV points after every battle, 50% speed stat.
Power Belt: +4 Defense EV points after every battle, 50% speed stat.
Power Lens: +4 Special Attack EV points after every battle, 50% speed stat.
Power Band: +4 Special Defense EV points after every battle, 50% speed stat.
Power Anklet: +4 HP EV points after every battle, 50% speed stat.