Assuming you don't want to use Legendaries, here's a pretty decent lineup:
1: Ninetails / Arcanine / Charizard (fire)
2: Alakazam (psychic)
3: Gengar (ghost)
4: Venasaur (grass / poison)
5: Pidgeot (flying)
6: Raichu / Jolteon (electric)
7: Vaporeon / Lapras (water / ice)
So yeah, that's about it for what you would need or even want on a team. Ground/Rock really isn't important, and neither is fighting, however... Hitmonchan is the BEST Pokemon of all time, since it can learn Fire, Ice, Electric, and Fighting, so that's another great option.