Homestayweb
http://www.homestayweb.com/
Center for Culture Interchange
http://www.cci-exchange.com/travelabroad/program.aspx?id=868
Homestay in Japan
http://www.homestayinjapan.com/index.html
A in J Fortune (Sapporo, Hokkaido, 8-15 day stay)
[with or without courses]
http://www.ainjfortune.com/ainjfortune-html.htm
PACE International
(English language section not complete)
http://www.pace-homestay.com/indexen.html
Japan Homestay Service (Chiba)
http://home.att.ne.jp/orange/star/homestay/index.htm
Homestay in Japan
http://www.homestay-in-japan.com/eng/program/homestay.html
Worldwide Homestay
http://www.worldwidehomestay.com/Japan.htm
Homestay Booking
http://www.homestaybooking.com/homestay-japan
JTB USA
http://www.jtbusa.com/en/other/o-homestay.asp
TAS
http://tas-japan.net/learn-about-japan/homestay-program
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Programs offering homestay and classes
LanguBridge Tokyo Summer Program
http://www.langubridge.org/tksummer.htm
Andeo International Homestays (Fukuoka, 2-4 weeks)
http://www.andeo.org/html/japan.html
A in J Fortune (Sapporo, Hokkaido, 8-15 day stay)
[with or without courses]
http://www.ainjfortune.com/ainjfortune-html.htm
Nacel International (Tokyo, 1 week, live-in tutoring)
http://www.nacel.org/cd/Home-Lessons/Japan.php
Hokkaido International Foundation
http://www.hif.or.jp/en/