Shinjuki has lots of big electronics stores, like other posters mentioned before BIC Camera, Yodobashi and also Sakuraya.
I've bought a digital camera in Shinjuku, at this time, about 2 years ago, the Sony P10 wasn't even available in Belgium. I payed about 59000Yen and got a voucher with it from 10% of the purchase price, which you could spend in the store (this was Sakuraya). When the Sony P10 first appeared on the Belgium market and on the Belgium Sony store website, it sold for more than 900€. So, if you're looking to buy a digital camera, you can certainly save a few euros and/ or buy a model that isn't even available yet in Europe.
When buying a digital camera you should be aware of the fact that not all camera's are there to be sold for export, meaning, only a small collection has the instruction books in languages other than Japanese. Also, at the time I bought a camera, all camera's came with guarantee only valid in Japan. On a positive note, because you're going to export the camera, when you bring your passport with you, you're entitled to buy it VAT free. All you need to do is show your passport, they will than staple the reciept in it, on departure in NRT
, show it to customs together with your camera.