Go to shopping; BicCamera

Though electronics stores are a dime a dozen in Tokyo and there are many brands and chain stores, my personal favourite is BicCamera for no real reason. Ｉｔ　ｏｆｆｅｒｓ nothing above and beyond other stores like Sakuraya, Nojima, Kojima, Yodobashi Camera, etc.

Like most stores they offer a loyalty card scheme where, in BicCamera’s case you can get up to 10% of the value of your purchase in points on your card, which can then be used for other purchases. The newcomer to Japan will have many things to buy, like washing machines, refrigerators, air-conditioners et all, so points can accumulate very quickly, allowing you to make some other purchases for "free".
Your first priority in Japan will be to select one of the many electronics stores and get yourself a points card.

For the visitors these stores also offer a good opportunity to ogle the many gadgets available to Japanese consumers as they stock a variety of items from kitchenware, massage chairs, games, consoles and audiovisual equipment to cameras, watches, jewelry, mobile phones and bedding.
Though the shops vary in size it would be worth checking their respective headquarters. BicCamera, for example, has its HQ in Ikebukuro, but I believe their Yurakucho branch, close to the Sony building, is one of the larger ones, and was the scene of the PS3 launch debacle earlier this month.
People looking for cheap electronics are better off searching the backstreets of Akihabara, but your average consumer looking for electronic skin cleansers, automatic hoovering robots or 50 inch television/computer hybrids can stay away from that den of geekiness and simply visit these regular electronic shops for regular people.

Location: Yurakucho station is on the Yurakucho line.
Website: http://www.biccamera.com/
Map for the Yurakucho branch or any of the others.