Daiso 100-yen shops
Daiso is one of the main retail chain stores of 100-yen shops, which are similar to 99-Cents stores in the US.
This website explains what a 100-yen shop is. Similar to convenient stores in the US, you can find anything from kitchenware to cosmetics to snacks, and much more.
A great resource for importing Japanese media. Oftentimes video games will come out in Japan long before the US or Europe, and Play-Asia is a great resource for day-1 buyers.
A great resource for Japanese pop culture items. J-Box offers snacks, manga, anime, clothes, and many more imports directly from Japan.
Online anime retailer that also features toys and figurines, which are very popular in Japan.
Asian Food Grocer
Important Japanese snacks and beverages. Here you can find a large inventory of the most popular Japanese candy, snacks, and ramen, as well as kitchenware items.