How about Sahoro, a Club Med resort in Japan?
I snowboarded in Korea Chuncheon last dec.. was awesome.. Though its peak period mid-late dec) the slopes were not as crowded.
Understand frm my cousin who's a tour leader, the usual popular picks in Korea (mostly in Seoul) would be really packed in Dec thanks to the Winter Sonata fans. Bad for beginners and especially dangerous.
Planning to go to Mt Bulla in Melbourne, Australia next June. Definitely more costly than Korea's but heard its lovely.
Cant recall the name of the korea one i went to. BUt if u need it, PM me.. i'll check it out for you.
Just boarded over Christmas at Phoenix Park in Korea, around two hours drive from Seoul. Not bad, a variety of slopes, not dangerous for beginners either as on the beginner slopes everyone is learning to board and half sliding down on the sides. There's a hotel there, which is where I stayed, tatami style. Have four sessions for skiing/boarding, one is even from 11pm - 5am! Hardly anyone out there at that time! And if you get bored at night, theres an arcade and a bowling alley as well.
Theres a Youth Hostel in the Park too, dunno about that though, should be cheaper.