Bic Camera is a Japanese electronics chain with a store right at Hachiko Plaza, a minute's walk from Shibuya station's scramble crossing. The store spreads across multiple floors and covers the full range of consumer electronics: cameras, computers, smartphones, audio equipment, home appliances, and gaming gear.
Prices are competitive, and the range is significantly broader than most Western electronics shops. If you are looking for camera lenses, headphones, or small appliances to bring home, this is a solid starting point. Staff can usually arrange tax-free purchases for foreign visitors — bring your passport.
The store also carries a decent selection of quirky Japanese gadgets you will not easily find elsewhere. Allow more time than you think you need.