Master Roshi's Island
This is a small island, where a turtle hermit and perverted old man, named Master Roshi lives. He lives on the island with a very, very old turtle that can talk, and Oolong since it seems he is always there.
People that trained here:
Goku
Krillin
Gohan

Kami's Lookout
This where the Guardian of the Earth lives, along with his assistant Mr. Popo. The lookout hovers high above Earth over Karin's Tower, on the lookout Kami can watch everything that is going on in the world. Fighters come here to train in the Room of Spirit and Time or the Hyberbolic Time Chamber. Which a fighter can go in and train for 1 day on the outside, but in inside 1 year goes by. You see the fighter do this is the Cell Saga before the Cell Games begin. In the Cell Saga, Dende becomes Guardian of the Earth when Piccolo & Kami fuse back together.
People that trained here:
Goku
Vegeta
Gohan
Trunks
Tein
Yamcha
Piccolo

King Kai's Planet
This is a small planet where the God of the North Galaxy lives with two other beings, Bubbles a monkey, and Gregory a Bee. King Kai is a little guy with great strength, but nothing that compares to Goku. The planet is a great Training place, because it is 10x normal gravity. In order to start training with King Kai, you have to make him laugh with a joke. Goku did it very easily, but Yamcha, Tein, Chaozu, and Piccolo had a hard time at this.
People that trained here:
Goku
Piccolo
Tein
Yamcha
Chaozu

Gravity Capsule
This is a special Space ship that was created by the Capsule Corp, that you can change the gravity inside the ship. Goku trains at 100x gravity in one on his way to Planet Namek, and Vegeta trains in one during the Cell Saga. Yamcha sort of trains in the one Vegeta trains in, but the gravity that Vegeta had it at was to much for him. He almost gets killed, but reaches the shut off button.
People that trained here:
Goku
Vegeta
Yamcha

Kaioshin's Planet
This is where the Master of all Gods lives. Don't know a lot about this planet, except it is where Gohan got the Zet Sword and became Mystic Gohan. I do think that Gohan is the only human that has gone to this planet.
People that trained here:
Gohan