Kareigawa no Yu

Kareigawa no Yu is a lovely higaeri (day-use) only bath that is a bit out of the way but is new, clean, stylish, and tucked right next to the historic Amori River.

Kotohira Onsen

Kotohira Onsen is a simple, family style day bath tucked next to a river.  A variety of rooms offer different baths, ranging in price from about 2000 yen to 3500 for 60 minutes.  As with most kazokuburos, the water is poured fresh each time, allowing you to add cold water if necessary until it's just at the temp you like.  Separate male and female baths are also available, and some nice rotenburo.

Edoyu

Edoyu is a great spot for people looking for an onsen experience without leaving Tokyo.  Though on the pricey side, Edoyu offers a variety of baths and a variety of other services (massage, etc).  Most unusual, it is open all night -- offering those willing to forgo a hotel a very reasonable overnight option.

Shoukichi no Yu

Located at the top of a steep, vertiginous road, Shoukichi no Yu is a simple place with unadorned grounds that verge on shabby, but it has a lot to offer, especially for larger groups. You could easily come here with a bunch of friends and feel like the place is all yours -- and the views of the valley are sublime.

Gero Onsen

For a large, industrial onsen town Gero's remarkably charming, perhaps because so much of the tourism is still onsen-based.

Takaragawa Onsen

Takaragawa Onsen is loads of fun, despite its being over-commercialized and even a bit weird. For starters, it is giant -- one of the biggest if not the biggest outdoor konyoku rotenburo in Japan.