Pokemon Diamond and Pearl Elite Four

Aaron

Dustox Level 53
BeautiflyLevel 53
Vespiquen Level 54
Heracross Level 54
Drapion Level 57

Bertha

Quagsire Level 55
Golem Level 56
Whiscash Level 55
Sudowoodo Level 56
Hippowdon Level 59

Flint

Rapidash Level 58
Steelix Level 57
Drifblim Level 58
Infernape Level 61
Lopunny Level 57

Lucian

Mr. Mime Level 59
Girafarig Level 59
Medicham Level 60
Alakazam Level 60
Bronzong Level 63

Champion: Cynthia

Spiritomb Level 61
Garchomp Level 66
Milotic Level 63
Gastrodon Level 60
Roserade Level 60
Lucario Level 63

On Aaron, bring a strong Fire, Flying, Rock, Electric, or Ground type. For Bertha, bring a strong Grass or Water type. For Flint, bring a strong Fighting, Water, and Ground type. For Lucian, bring a strong Bug, Dark, Fire, Flying, and Ghost type. For Cynthia, bring a strong Electric, Fire, Flying, Grass, Ground, and Ice type. Remember that her Spiritomb has no weakness, so just hit it with strong attacks.