Used manga represents possibly the greatest deal in all Japan. When I first went to Japan I was excited to get all of the anime I'd come to enjoy in the states. New CDs and DVDs are generally prohibitively expensive, over 3000 and 5000 yen respectively. However, used manga generally range from 100-300 yen. Moreover, unlike new manga, the used manga aren't sealed and you're able to look through them before purchasing.
This is a quick guide to what I consider one of the gems of Shibuya. When I first went to Japan I normally went to Book Off or other used book stores to get my used manga. They normally have a good selection and I was pretty happy. However, I started spending more time in Shibuya and I found several stores near the Beam which have a lot more to offer. These include Mandarake, Manga no Mori, and the J-Pop Cafe. Mandarake has the most extensive collection of collectibles, doujinshi, hentai, manga, video games etc. that I've found in Shibuya. I managed to find a Supergrafx with games for less than 10,000 yen, the entire LD set of Tekkaman Blade 2nd Season for less than 10,000 and a dozen other odd used goodies.
<Editorís Note: Damn! When Scott told me about the Sgfx deal, he didnít mention games!! Agh!! I shouldnít have passed that up! *ahem*. Sorry for the disturbance.>
Manga no Mori (The Comic Forest) is located directly across the street from Mandarake. Carrying only new manga, this is a great place to pick up odd titles. I've seen advertisements for it when watching anime and I believe there are several locations in Tokyo. Still, since it's right across the street from Mandarake it makes a convenient trip.
Finally, the J-Pop Cafe is upstairs in the Beam. This one comes highly recommended by Japanese friends. It's a cafe that has a living room like decor and provides access to an updated collection of J-Pop for patrons to listen to. It's cheap generally a great place to just chill.
Also, all these places are located in/around the Beam. The Beam has a Namco arcade on the ground floor and a great Shabu-shabu restaurant as well so check these out too.
Anyways, let me see if I can get you to all these places. They're pretty close to each other, but shibuya's not the easiest place to get around. To start with, check out this map. You can see the Shibuya station and the Beam in the lower left corner.
You're going to need to walk with Starbucks on your left past Seibu A. Take a left (The street name is Inokashiradoori, but you won't see any signs. Just including it for your reference ;) Cool detour by Zara is up Spain street. It's a cute little street with a great crepe shop at the top.
Walk past the HMV and everything and the road will split at a Police Box (Kouban). Go to the right. (At the corner to the right is a really good Indian restaurant called the Taj Mahaal or something like that. My Japanese professor claimed it was his favorite restaurant in the world.)
On the right you will see Manga no Mori.
To the left, Mandarake. Mandarake is at the bottom of a long set of stairs. You'll have to put your bags and stuff into lockers and you're not allowed to take pictures inside.
From the entrance of Mandarake, look up and to the left. Here's a sign for the J-Pop cafe.
Also, for the return trip, try this out. Walk past the Beam and take a left. Walk until the road dead ends (on Bunkamura dori. Again, there's no signs for this street, but it has a Citibank, Segafredo and is pretty central. Take a left. On the left side of the road you'll pass a little ramen store that is normally packed. It's called Hokkaido Ramen and serves the northern style ramen. It's good and cheap. Try the Iron Fire Ramen (I don't remember the name exactly) if you like spicy things.
Views looking up,
and down the street from Hokkaido Ramen.
Mandarake's map to their store.
Their english page.
Also, just a big listing of resources in the area.
Hope this helped...enjoy!