Turning right onto Chuo doori and walking a few meters, we make it to our first stop - the famous MediaLand (formerly Zet). Everyone seems to know about Zet; I've talked with people around the world who've heard of this used games and collector's store. But, for some reason, fewer people realize that they changed their name a year ago.
Of interest to all of us would probably be the second floor, of course. The floors are mostly laid out in the same way: The entrance is by the staircase, and there's a small hallway-style opening where hardware and boxed software is displayed. Passing that, you enter the main room with a cashier, shelves of boxed games lining the wall, a guy on a stand barking thanks to customers and occasionally BSing with the cashier, and a wagon in the center with loose and boxless games.
Famicom and Disk System games are to the left of the cashier, lining the wall on the second floor. Feel free to browse as much as you want, although don't come on the weekends if you can help it since it gets difficult to move around. The Famicom scene in Japan has progressed to the point where prices for the most desired games have pretty much been "set" by the used games stores. As a result, the only way to find some games for cheap is in the out-of-the-way spots (ie. not Akihabara). Don't be surprised to find things like Castlevania III going for 5300 yen, Mother for 4000 yen, Zanac on Disk System nearing 10000 yen, and so on.
A great by-product of this used games biz, though, is the fact that condition dictates pricing. If something looks brand new, then it'll be sold at a price reflecting that. If the box looks worn, someone wrote passwords in the instruction manual or whatnot, the price will go down. This is the secret to getting things like Final Fantasy II or III complete for 700 yen or so - what I would consider "a slightly worn box" makes MediaLand pricers deeply discount the cart.
MediaLand has a tendency to get very large quantities of games in, sell them for cheap, and blow them all out of the store in less than a week. If you decide to not buy something it'll probably be gone the next time you pay a visit. I made this mistake with a special-edition of TM Network Live In Power Bowl that was around 1000 yen (for sake of comparison, other stores sell the same thing for over 4000).
Head to the fourth floor for a laugh. MediaLand coined the term "premiere game" to mean "game they can sell for over 10,000 yen" - and now they put those games in a stand here. Ever-prevalent are Game and Watches (they all go for over 8000 yen here), various limited-edition software, and the anime extravaganza adventure Metal Slader Glory - 12,000 to 25,000 yen depending on completeness and condition. These games aren't necessarily rare - just extremely sought after by people too lazy to search for themselves. They're out there in the fleas if you bother to look, and at least one magazine has published articles about how to profit by buying "premiere" software at the fleas and selling it to MediaLand and the like for bucks. That's one way to support your hobby, I suppose.
Although you shouldn't make it a habit of buying software here, MediaLand is worth a visit and proof enough that the Famicom has made its mark on the gaming world in Japan.