Just a small suggestion about Yokohama
Shopping: World Porters, Queens Square, Landmark Plaza and the red brick house
Sight: China Town, Ramen Museum, Landmark Tower observatory (Amazing view)
Entertainment: Cosmo world (over rated), cup noodle museum - I've never been to the one in Yokohama, its new, but I've been to the one in Osaka, and it was fun..... you should be dine in an hour or so
Eat: MANY MANY choices all arounnd
I strongly recommend Yokohama, partially because its my favourite place (And I practically grew up there).....
Odaiba is also a must for shoppers like you. There are just way too much to do to skip Odaiba for a first timer...
Harajuku is also a must for you, takeshita dori (Right infront of the Harajuku station) is filled with local fashion and teenagers.
EDIT: This is a great site for you to plan your days in Yokohama
Yokohama Visitors' Guide