Re: Death Valley?
I'm not sure if I could make it David, but I believe that December is a reasonable time to visit. February/March is a period with rain and/or dust storms, and late April through about October is probably too hot (<A HREF="http://www.nps.gov/deva/Pdf/Weather.pdf">weather info.</a>). You should also note that 80% of the roads in Death Valley are unpaved, so to see the best of the place you need a high clearance vehicle. For example, to see those sliding stones you need to travel about 20-30 miles off road.
As an alternative, you could also consider King's Canyon or Sequoia. These are, however, pretty much inaccessible by a vehicle, though are good for a back-country trip. Further north you have Highway 395 which runs along the eastern side of the Sierras, and has a number of great photography locations. It's at altitude (up to 9000ft) though, but they keep it pretty clear during the winter so that skiiers can get to Badger Pass.
A bit further north (on 395), you have Mono Lake (fabulous) and Yosemite. Mono Lake is in the 'high desert' which doesn't mean sand dunes, but rather a lot of scrub like the Navajo areas in Arizona. The lake itself is wonderful though (I took a photo workshop there last January). Again, because it's at altitude it can be very cold (10-20F max during the day at that time of year).
You can only access Yosemite Valley (i.e. not the whole park) by car in December. Highway 120, which runs east/west (with Mono Lake at the eastern end) is closed from about October through to May because of snow.
Please let me know if you need any more information. I'll keep this one in mind.