A good ground type in Heart Gold or Soul Silver would be Nidoking. Nidoking is ground-poison. you can find Nidoran male at route 35.
Steelix is a good Steel type Pokemon. It is also a Ground type, too.
Vermillion City (kanto)-Lt. Surge Electric Type- mid 40s to low 50s. Ground Type Pokemon great against this gym.
Psychic and Ground
I liked hoot hoots evolved form noctowl and pidgeot where good. Ground type I liked diglett and sandshrew.
Water type moves and Grass type moves. Electric moves will have no effect. Flying types and Pokemon with levitate ability are good as ground-type moves have no effect against them.
Steelix is a good Steel type Pokemon. It is also a Ground type, too.
If you are playing heartgold or soulsilver , you need a physic or ground type pokemon.
Fighting and Ground type moves are most effective against dialga, since it is a dragon+steel type pokemon.
Vermillion City (kanto)-Lt. Surge Electric Type- mid 40s to low 50s. Ground Type Pokemon great against this gym.
In HeartGold you can catch Kyogre.
All you need is a ground type pokemon or a ground type move
Psychic and Ground
I liked hoot hoots evolved form noctowl and pidgeot where good. Ground type I liked diglett and sandshrew.
A grass type, A ground type, A fire or flying type or both, A psychic type, A water type/ground type/rock type, and any legendary.
Water type moves and Grass type moves. Electric moves will have no effect. Flying types and Pokemon with levitate ability are good as ground-type moves have no effect against them.
Fighting type, ground type
Fire, Ground, and Rock.