Gogeta is Vegeta and Goku fused together. To become Gogeta Vegeta and Goku must perform the fusion dance, which is also used by Goten and Trunks to become Gotenks. The fusion dance looks silly, and often messes up. For instance Goku and Vegeta once ended up as Fat Gogeta, the same thing happened with Trunks and Goten too. Gogeta is a very strong warrior who killed Janemba. But the coolest thing about Gogeta is his voice. He sounds like Vegeta and Goku. It's like a split voice. Gogeta never went super saiyan 3, unlike Gotanks, but he can still go SSJ.

Vegetto is the strongest fusion form of Goku and Vegeta. But in order for Goku and Vegeta to become Vegetto, they have to put on the fusion earrings. Vegetto is mostly Vegeta and he uses all of Vegeta and Gokus attacks.

Gotenks

Gotenks is the combined form of Goten and Trunks. He is super strong. He was also able to go Super Saiyan 3. Gotenks is formed when Goten and Trunks perform the fusion dance, just like Goku and Vegeta did to form Gogeta.

Piccolo has fused with Kami and Nail, man it must be crowed in Piccolos body. When he fuses with Nail, nothing fancy happends, but when he fuses with Kami, there is a big light explosion, but other than that nothing special happends to piccolo. When he fuses with nail and kami, he doesn't learn any new attacks, but his strength increases greatly.