Here's the leader, location and pokemons of the leaders:
Roxanne, Rustboro City, Geodude lvl.12, Geodude lvl.12 and Nosepass lvl.15.
Brawly, Dewford Island, Makuhita lvl.19, Meditite lvl.16 and Machop lvl.16.
Wattson, Mauville City, Voltorb lvl.20, Electrike lvl.20, Magneton lvl.22 and Manectric lvl.24.
Flannery, Lavaridge City, Slugma lvl.24, Numel lvl.24, Camerup lvl.26 and Torkoal lvl.29.
Norman, Petalburg City, Vigoroth lvl.27, Slaking lvl.31, Spinda lvl.27, Linone lvl.29.
Winona,Fortree City, Swablu lvl.29, Tropius lvl.29, Skarmory lvl.31, Pelliper lvl.30 and Altaria lvl.33.
Liza & Tate, Mossdeep City, Lunatone lvl.42, Solrock lvl.42, Xatu lvl.41 and Claydol lvl.41.
Juan, Sootopolis, Luvdisk lvl.41, Kingdran lvl.46, Sealeo lvl.43, Crawdaunt lvl.43 and wish cash lvl.41.
Just a hint in the 7th Gym have Pokemons at least at lvl.50 because I reached the end of the game twice and I must say for me it's the hardest gym.
Hope it was useful.
[Edited by ArchDuke, 9/20/2008 8:25:14 PM]