Outdoor Japan focuses on hot springs located in remote, natural settings. The listings are brief but cover a healthy number of onsen near Japan's major cities.
This personal site, Hot Springs Michelin, focuses on onsen that are close enough to visit on day trips from Tokyo.
Readers, meet Yoshiko. Yoshiko is from Aso, a volcanic region of Japan peppered with onsen. And welcome to her charming site filled with listings, many good photos, and Yoshiko's often quirky one-liners. Yoshiko's Favorite Places makes for entertaining reading and will make you want to head directly to Aso to visit the local hot springs.
Excellent descriptions of some 50 onsen sites in Japan. The site's author, Jens Olsen, has indexed Free and Other Hot Springs of Japan by location and type of onsen. Jens breaks out hot springs based whether the onsen described requires hiking, requires that you dig your own pit (yes, it is possible), are free, or allow mixed bathing. Jens' detailed descriptions will help you quickly decide which onsen is right for you.
Don't let the rambling prose and choppy design turn you off from Ed Jacob's Quirky Japan Homepage. Filled with wonderful hi-res art of onsen (and other scenes from Japanese life), this site will whet your appetite not only for visiting hot springs, but for just being in Japan. Many unusual links will keep you busy reading for hours and hours.
Navigation could be improved, but the information on the Japan National Tourist Organization site never stops comin' at you. Plenty of links to other official sites means you should bookmark this site and consult often.
A link to ATMs worldwide, according to Visa International Service Association.
Want to know what to expect from a stay at a Japanese ryokan? The Japan Ryokan Association web site will put your mind at ease.