Berries, they help your Pokémon in battle and help raises their contest status. The Berries are only obtainable through Wild Pokémon, a Berry Man or by Trading with Ruby/Sapphire/Colosseum.
Here you will find a list of all the berries and what they do:

Picture:	Number:	Name:	Effect:	Location:
	#01	Cheri Berry	Heals Paralysis	S.S. Anne/Pick-Up Ability
	#02	Chesto Berry	Heals Sleeping	S.S. Anne/Pick-Up Ability
	#03	Pecha Berry	Heals Poison	S.S. Anne/Pick-Up Ability
	#04	Rawst Berry	Heals Burn	Pick-Up Ability
	#05	Aspear Berry	Heals Frozen Status	Pick-Up Ability
	#06	Leppa Berry	Recovers 10PP to an attack	Pokémon Jump Prize
	#07	Oran Berry	Recovers 10HP	Pick-Up Ability
	#08	Persim Berry	Heals Confusion	Pick-Up Ability
	#09	Lum Berry	Heals Any Status Condition	Pokémon Jump Prize
	#10	Sitrus Berry	Recovers 30HP	Pokémon Jump Prize
	#11	Figy Berry	Recovers 1/8 HP and confuses any Pokémon that doesnt like Spicy Flavour	Pokémon Jump Prize
	#12	Wiki Berry	Recovers 1/8 HP and confuses any Pokémon that doesnt like Dry Flavour	Pokémon Jump Prize
	#13	Mago Berry	Recovers 1/8 HP and confuses any Pokémon that doesnt like Sweet Flavour	Pokémon Jump Prize
	#14	Aguav Berry	Recovers 1/8 HP and confuses any Pokémon that doesnt like Bitter Flavour	Pokémon Jump Prize
	#15	Iapapa Berry	Recovers 1/8 HP and confuses any Pokémon that doesnt like Sour Flavour	Pokémon Jump Prize/Berry Forest
	#16	Razz Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#17	Bluk Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#18	Nanab Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#19	Wepear Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#20	Pinap Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#21	Pomeg Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#22	Kelpsy Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#23	Qualot Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#24	Hondew Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#25	Grepa Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#26	Tamato Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#27	Cornn Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#28	Magost Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#29	Rabuta Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#30	Nomel Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#31	Spelon Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#32	Pamtre Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#33	Watmel Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#34	Durin Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#35	Belue Berry	Plant in the Earth to grow Berries for Pokéblocks	Dodrio Berry Picking Prize
	#36	Liechi Berry	Raises Attack when HP is below 1/3	Ruby/Sapphire
	#37	Ganlon Berry	Raises Defense when HP is below 1/3	Colosseum
	#38	Salac Berry	Raises Speed when HP is below 1/3	Colosseum
	#39	Petaya Berry	Raises Special Attack when HP is below 1/3	Colosseum
	#40	Apicot Berry	Raises Special Defense when HP is below 1/3	Colosseum
	#41	Lansat Berry	Raises Critical Hit Ratio when HP is below 1/3	Emerald
	#42	Starf Berry	Raises Any Stat when HP is below 1/3	Emerald
	#43	Enigma Berry	Morphs into E-Reader Berries	Ruby/Sapphire