Hayato -
Here's the first gym leader. In the gym, you'll find some easy trianers with bird pokémon, and the gym leader having a level 7 Pidgey and a level 9 Pidgeotto (easy stuff). You will get the Wing Badge which allows you to use Flash anytime, TM31, and $900. Watch out if you started with the leaf pokémon, becuase he will have some problems against birds.

Tsukushi -
Here's the second gym leader. In this gym, you'll be fighting bug pokémon. The leader has a level 14 metapod, a level 14 kakuna, and a level 16 scyther. You will reward you with his Insect Badge which lets pokémon up to level 30 obey you, TM49, and $1600

Akane -
Here's the third gym leader. The gym here uses normal pokémon. Fighting pokémon should rip this gym up. Akane, the leader, uses a level 18 Clefairy and a level 20 Mirutanku. She gives you the Regular Badge, TM45, and $2000. Before she gives you the badge talk to the trainer below her, and then talk to her.

Matsuba -
Here's the fourth gym leader. This city has a gym that specailizes in ghost pokemon so a psychic pokémon would help here. The leader has a level 21 gastly, a level 21 haunter, a level 25 gengar, and a level 23 haunter. The leader rewards you with the Phantom Badge which allows all pokémon up to level 50 obey you, TM30, and $2300.

Shijima -
Here's the fifth gym leader. Battle the gym leader, who uses fighting types. He has a level 27 primape and a level 30 poliwrath. He rewards you with the Shock Badge which allows all pokémon up to level 70 obey you, $3000, and TM01. Before you leave, talk to all the people in the town. One person will give you HM 02, or the Fly HM, and another will activate the 6th Gym Leader to come down from her tower to fight you.

Mikan -
Here's the sixth gym leader. Go back to the "Steel" gym, where you'll only find the gym leader (no junior trainers!). She has two level 30 magnemites and a level 35 Haganeru(#208) or "Steel Onix". She rewards you with the Steel Badge, TM23, and $3500. She won't be too hard to beat.

Yanagi -
Here's the seventh gym leader. Hit the seventh gym, which is an ice gym. The leader has a level 27 seel, a level 29 dewgong, and a level 31 Inomu(#221). He rewards you with the Ice Badge, TM16, and $3100. A fire type will roast the place up. Once you have the 7th badge, you only have to get one more!

Ibuki -
Here's the eigth gym leader which leads a dragon gym, where you'll again have to push down boulders from above to step over the lava to the leader. The leader is rather powerful, and has 2 level 37 dragonairs, then a level 31 Kingudora(#230), and a final level 40 dragonite. The leader won't give you the badge right away, but she'll give you $4000. To get the Raging Badge, surf behind the gym and enter a cave. Once inside the cave, you'll have to get past a whirlpool, so bring along your Pokémon that has HM06 equipped. Once you find the lone Pokéball and pick it up, Ibuki will come along and give you the Raging Badge. Now all Pokémon will obey you. She'll also give you TM24.