Fukuoka:

Guest House Hokorobi – http://house.cocosys.co.jp/
Guest House Kaine – http://www.kaine-g.com/
Aza Fukuoka Seminar House – http://aza-fukuoka.com/
Fukuoka Hana Hostel – http://fukuoka.hanahostel.com/
Guest House Nakaima – http://guesthousenakaima.wix.com/nakaima
Hostel Takataniya – http://takataniya.com
Khaosan Fukuoka Annex – http://www.khaosan-fukuoka.com

Japan:

Japan Youth Hostel Guide – http://www.jyh.or.jp/e/index.php
Japan National Tourism Organization – http://www.jnto.go.jp/eng/index.html (“Plan your trip”)

Please leave suggestions in the comment section.