I had recommended often going to Big Daiso(Japan guide) in Machida before. Unfortunately that Daisoo was closed, but 100yen Shop in Japan is getting better and better, actually some shop seems to have speciality.
Daiso is the biggest one, there are 2700 shops in Japan and also 700 shops in abroad. From foods to DIY tools, they cover various type of products, when you visit the big Daiso, it is hard to find something they DON'T have except for expensive jewelly and closethes :-)
No2.is Seria. Their concept is very clear, it's "For Ladies". Basically their products are natural, simple and cute, so we can use thier stuff that as is, but it doesn't look 100yen at all.
Small strage is the strongest pruducts of 100yen shop and Seria's prodcuts are cuter more than other shops, like this wood box, plastic box, iron, box etc at . Wall decor stuff does't looks cheap too, Do you think this Wall Sherf tin plate, iron fuck look 100yen? Bowls, cups, eating utensils are cute too. This is Fire Kingish one, Japanese design or other design one, and these are very simple so even guys love them.
The hottest part of Seria is people enjoy remaking into some original stuff by DIY with their own idea. There are a huge number of pages "remake Seria products" in NAVER. Wood board, Drawer box, wood case, those are most popular DIY item. Since Seria has Stencil sheets, paint, varnish etc,. too, it's very easy to decorarte. And guess what! Those Stencil sheets are Heat-resisting, you can make original mug cup too.
With your creativity, imagination and some small DIY skill, you will be able to make a lot of original good things. People recommend each other the stuff they like and find in Seria. Please check it out and don't miss going there when you come to Japan. Seria is really usuful and nice shop