Yosemite was our featured destination in the spring, too - but it changes so much with the seasons that it's the best place we can think of for a December (or later winter) trip.
The last time I was there in December, we traveled up into the valley just after a small snowstorm, right after the roads were cleared. By noon the next day, the winter wonderland had melted, but we found the park blissfully un-busy, and with a lot of things to do. As a bonus, lodging prices are also lower in Yosemite in the winter.
Our guide to Yosemite in Winter will help you know what's open, what's not, and what special activities are available.
If you can't go now, take a look at these pictures to see what the park looks like covered in snow.