Seibu
Two of Tokyo's major department store/railroad conglomerate chains, Seibu and Tobu, are based in Ikebukuro and the stores here were not long ago the largest in the world. Paradoxically, Seibu, which roughly means "west Tokyo", is on the east side of the station, while Tobu, which means "east Tokyo", is on the west side.
Tokyu Hands
1-28-10 Higashi-Ikebukuro
10AM-8PM
next to Sunshine 60
A crazy 7 story 'DIY' store with floors of kitchenware, bath accessories, paper goods, scrap-booking supplies, tools, hardware, exotic woods, travel supplies, toys, pet supplies, and Nekobukuro on the top floor. This is a place where you can find, for example, lava lamps next to a shark suit next to a Gundam model.
Bic Camera
This discount retailer's flagship store on the east side of the station, with several branches nearby.