Blue Mountain No.1 is really good but even better at the course.
Coffee is really popular in Japan and one can find a coffee bean shop in pretty much any decent sized town.
The most populart high end coffee bean in Japan would be Blue Mountain No.1 (200g going for 4000 - 7000 JPY)
Hawaiian Kona Coffee (Extra Fancy) is also popular but pretty rare (200g going for 3000-5000 JPY).