Discussions about the first Kamen Rider of this century, who has the second most forms, go here.

Kamen Rider Kuuga Growing Form
Kamen Rider Kuuga Mighty Form
Kamen Rider Kuuga Dragon Form
Kamen Rider Kuuga Pegasus Form
Kamen Rider Kuuga Titan Form

Kamen Rider Kuuga Rising Titan Form
Kamen Rider Kuuga Rising Pegasus Form
Kamen Rider Kuuga Rising Dragon Form
Kamen Rider Kuuga Rising Mighty Form
Kamen Rider Kuuga Amazing Mighty Form
Kamen Rider Kuuga Ultimate Form

Added Kuuga's other forms above.