While seeming somewhat out of place in trendy, youth oriented Harajuka, the Oriental is a great one stop shopping place. There are several floors that sell typical tourist items, textiles, dolls and pottery, etc., along with some nicer things like woodblock prints. I didn't thing the prices were any different than in other parts of Tokyo; this was just a good place to have everything together.
What to buy: Typical tourist trade, along with handicrafts and some finer items. There is furniture on the top floor - some really nice looking antique pieces - but good luck if you can fit anything into your suitcase for the trip home.
What to pay: Average prices.
Although Tokio is, I would say, a very touristy spot, finding a place that sells common stock viewcards seems to be a rather challenging task. It appears that some gift-selling establishments are most likely to stock them. No cards in bookstores or post offices. Two spots I've seen them are: Oriental Bazaar (Omotesando) and the gift shops of Asakusa. Good luck!
There's a huge number of souvenir stalls on the way from Asakusa subway station to Sensoji. You should be able to find something to suit your needs.
If you are a fan of Peko Poko girl, the cartoon girl, this is the place to buy your souvenirs. It is also a bakery and cafe where you can savour mouthwatering cakes and sipping freshly brewed coffee.
There is a souvenir street right outside of Senso-ji Temple. Many small souvenirs and snacks can be found along this pedestrian street.