My Barbaric Girlfriend

From Tokyopop:

A rude girl and an effeminate boy switch bodies and find that it might be a better fit for both of them in this crazy comedy:

Nanako Momoi is the belle of high school... as long as she stays quiet. Once she shows her true self, guys' dreams are shattered for she is a true tomboy. Akira Uehara has the looks and brains, but, unfortunately, his personality is so dull it overcasts a shadow, and nobody notices him.

One day, Nanako's grandfather comes up with a crazy invention, and Nanako and Akira trade bodies! She's in his body, and he's in hers!