The west side is shopping heaven. There are some great cultural and tourist-friendly sights as well, but the shopping, oh, the shopping. Most of the districts that I'll cover are pretty much in a straight line running from Ikebukuro in the north, down through Shibuya in the south. Both JR Yamanote line and the brown Metro Fukutoshin line run right through this sequence of metropolitan madness.
The order goes:
Shinjuku (JR)/Shinjuku-Sanchome (Metro)
Harajuku (JR)/Meiji-Jingu Mae (Metro)
Lastly, Nakano Broadway, the hidden geek wonderland of resale stores, is located just west of the string between Ikebukuro and Shinjuku.
Topics Covered: Ikebukuro, Shinjuku, Harajuku, Shibuya, Nakano
That was all in one morning (though admittedly, it was from New Years Day sales). No regrets.