Many people have asked me how hard it is to order stuff from the Japanese Amazon.com site. It's become much easier as of late, now that many of their prompts show up in English. But what's been traditionally much harder is ordering used items, since many sellers over there don't ship internationally.
I've compiled here a quick guide to finding items you like on Amazon.co.jp, and finding used copies that you can order typically at fairly hefty discounts. Be warned that discount / economy shipping to the U.S. from Japan can still run as much as $6-$10, but it's still better than the $18 or so that you might nominally be charged for expedited shipping.
First, if you haven't done so yet, go register a new account in Amazon.co.jp. Your existing U.S. Amazon account will probably not work. Go to the main page, select "In English" at the top right, and then create an account by following one of the English prompts. If you see a "Want to see this page in English?" prompt on a product page after you do this, click that and all product pages from then on will have most of its information displayed in English.
Get the ISBN of the product you want to search for. This is nothing more than the barcode number, so as long as the product is barcoded you're in good shape.
Go search for the barcode number by using the search box at the top of the page. If you've set your account up for English as above, you should see the search box show up in English.
Go to the product page and click on the "X used from ¥XX" link to go to the list of people offering the item used.
Now comes the slightly tricky part. Search through the page for the following string:
This means "Shipping is available to other countries" (apart from Japan).
Find a seller that has this listed in the item description — start with the lower prices! — and then add that to the cart. (If you see a gold checkmark and the text 低価格商品, that means "Lowest Price".)
The column labeled コンディション is the item condition. 中古商品 - 良い means "Used - Good"; 中古商品 - 非常に良い means "Very Good".
Also try to pick a vendor with a good reputation — if you click on the link next to the vendor's reputation score (the gold stars) you'll get an English-language assessment of their feedback.
Bear in mind that if you don't pick from a seller that offers international shipping, your order will be rejected as unshippable. Also note that not all items will be offered from people willing to ship internationally anyway, so check back often.
Once you get to the last stage before checking out the contents of the cart, you'll be able to see the yen cost. You can figure out what this is in U.S. dollars by using an online currency converter, since the final charges will be listed in yen and not dollars. Typically ¥100 = $1, but it fluctuates, so check before shipping.
Place the order, then sit back and wait.
I'll be updating this guide from time to time as need dictates.