Bokura no Chikyuu no Arukikata

(from Tokyopop): Super serious Asahi Suzumura and laidback, easygoing Mitsuki Sayama might seem like an odd couple, but they made a deal; they'll vacation around the world and when they get back to Japan, they'll get married.

As they travel from country to country, the different people, cultures and cuisine they encounter begin to bring them closer together. After all they're not just learning about the world, but about themselves too.