If you have been to Hokkaido, consider spending your next winter trip in Tohoku.
For onsens, there is beautiful Ginzan Onsen village. Other popular onsen destinations include Nyuto Onsen, Naruko Onsen, Zao Onsen, etc. There are 2 onsen places which are famous for sunrise and sunset view, but I do not know their English names. Take a look at these:
http://www.mkanyo.jp/ (for sunrise),
http://www.furofushi.com/ (for sunset)
For scenery, there are 3 beautiful lakes, Tarawa-ko, Towada-ko with Oirase Stream and Inawashiro-ko which is filled with lovely swans during winter. For landscape, there are spectacular Geibikei Gorge, Gembikei Gorge and Naruko Gorge. A unique winter scenic destination is Zao-san where people make special trip up there to see the eice-tree monsters'. If you are into skiing, you can ski among them. They are even lit up at night. And of course, there is the ever popular scenic cruise in Matsushima.
For temples and shrines, Yama-dera is spectacularly perched against the hilltop. To hike up the steep steps when there is snow, straw is provided for you to tie around your shoes to ensure a firm grip. In Hiraizumi there are Motsu-ji and Chuson-ji whose golden hall, Konijiki-do is said to be Japan's first designated national treasure.
For history, go to Aizu-wakamatsu and the Tsuruga Castle if you are interested in samurai. Near Aizu-wakamatsu is the village of Ouchijyaku whose lovely setting overrides its historical significance. With its threaded rooftop houses, it is a sort of gShirakawa-go in the northh. Kitakata has lots of preserved kura storehouses. For archaeology, do not miss the Sannai-Maruyama Iseki site in Aomori.
For food, Sendai is famous for grilled ox tongues, Matushima for fresh oysters, Kesennuma for shark fins, Kitakata and Morioka for ramen, Yuzawa for udon and Aomori for apple.
For scenic train rides, the special line between Akita and Hirosaki/Aomori along the coast has special tatami viewing seats. Another special train ride is in Tsugaru, Aomori Prefecture where inside the former steam train compartment is a stove which food is grilled and you can enjoy hot buns or fry squids during the journey.
For winter festivals, there are many. Among them are Kamakura Snow Hut Festival in Yokote (Feb 15-16), Iwate Snow Festival in Koiwai Fram near Morioka (Jan 31-Feb 8), Hirosaki Castle Snow Lantern Festival (2nd Thurs-Sun in Feb), Memorial Snow Lantern Festival in Yonezawa (Feb 14-15), Innkko Matsuri Dog Festival in Yuzawa (Feb 9-10) and Snow and Light Fantavista in Towada-ko (Jan 30-Feb 22).