Most sprites, backgrounds and artwork: official pokémon art from Bulbapedia.
Black & White-style sprites of pokémons from generation 6 and above, including mega-evolutions, gigamax and regional forms: the Smogon Community's sprite project.
Pokémon cards scans: Poképédia and Bulbapedia.
Pokémon HeartGold-SoulSilver font: KastovianMan.