One of the things you often hear in photo forums is that you don't need to worry about your in-camera white balance settings when you shoot RAW - you can always come back later and adjust the white balance on your computer. Technically, you can do that, but I've found that the best way for me is to set up everything on my camera as if I was taking a very important JPG-only picture. If its a bright sunny day, I'll use "daylight" or auto-white-balance (auto usually makes it a bit too blue for my taste, but I try it anyway). If its cloudy, I'll use "cloudy", etc.
Back at my computer, the first thing I do when I process a RAW photo in ACR is choose the "as shot" settings. Theoretically, you should get a photo that matches your small JPG (if you shoot "RAW + JPG" in your camera). Usually, this produces the best results right off the bat. If I'm not happy with that, I'll try "daylight" or "cloudy" - I'll try them all. I've never been happy with "auto" in ACR - it never seems to work well. To fine-tune the white balance, I'll try different settings on the Temperature bar.
For even further fine-tuning, I like to use the gray point picker on the Levels or Curves dialog box.
