To get the best prices you should leave the big buildings behind and check out some of the little streets, where the smaller independent shops can be found. Many of these shops don't have the space to put their products on show and are more like a big warehouse where you have to ask the staff.
Getting the best prices
A website that might help you to get the best price is Kakaku. here you can compare the prices in all the different shops in Japan. The best way to use the site is to search the product and then put the address into a Japanese-English translator such as google's
It's not easy, but with the name and address of the shop, anyone will help you to find the shop. You could save up to 30%.
Before buying you should make sure the product has an international guarantee or not. Some products, such as some digital cameras, come with a guarantee only valid in Japan.