Spiralling Serial Spheres

The user creates two Rasengan, one in each of their hands. The user can then either attack two targets at once or attack the same target with both Rasengan.

Senjutsu Version
When in Sage Mode, Naruto can use a senjutsu-enhanced version known as. It is fundamentally the same as the normal version, except stronger.

Nine-Tails Influence
While using a combination of Kurama's chakra and senjutsu chakra on his Spiralling Serial Spheres, Naruto use's a technique known as Rasen-Rampage that is bigger than its regular version and can withstand a series of Toneri's Truth-Seeking Ball attacks.

In Naruto the Movie: Legend of the Stone of Gelel, Naruto creates a variation of this technique called Twin Rasengan (ツイン螺旋丸, Tsuin Rasengan) by enhancing one of Rasengan's with Kurama's chakra and the other with energy from the Stone of Gelel.

Trivia

 * Jiraiya does something similar when he teaches Naruto how to use the Rasengan; in one hand he forms a regular Rasengan, and in the other he does the balloon exercise.