I thought that I would write up some thoughts for today about 'White Balance'. I believe white balance to be very underestimated by many photographers. This is because many photographers just leave their white balance on 'auto white balance'. I believe some photographer's do this purely based around the effort of changing it and believing it has little effect when it is changed.
However I play with white balance a lot and believe it is a great tool to improving your photography. I change the white balance based on the conditions and lighting of my surroundings. If it is a very bright sunny day I will shoot with the white balance set to sunny, and if I use flash I will set the white balance to flash etc. I follow the lighting as best as I can. White balance is very easy to change on a DSLR, with my Canon 40D I simply hold a button and spin a dial quickly, its very easy and effective when I do so.
One of my most favourite examples of how white balance can affect your images is shown below.

I was out shooting in a forest when I saw this lovely green moss on the base of a tree. I was shooting with 'auto' white balance to see what results I could pick up. This was the initial shot I produced. (Note, both of these images are taken straight out of camera with no post processing or photoshop techniques applied.)
As you can see the image looks very 'muddy' and would require a lot of post-processing or photoshopping work to make it look more natural to its full potential. The colours look false and dim and I did not like the effect the image produced.
So next I decided to change the white balance from 'auto' to 'cloudy'. It was a very overcast day and this white balance suited the lighting conditions nicely. This next photo was taken moments after the first shot with 'auto' white balance, with the same camera, lens, shutter speed and aperture value. The only thing I changed was the white balance to the 'cloudy' setting.

From this photo you can see a huge difference. The 'auto' settings got the white balance completely wrong. From turning a wheel on the camera quickly you can see the dramatic difference that has occurred. The photo has improved drastically. The colours and warmth of the photo are correct even without post processing or photoshopping.
I highly recommend changing white balance settings in camera as they really help improve your images. My example shows this well and I could not believe how amazing the difference was when I changed it initially. White balance may seen as something you can correct easily when photoshopping or post-processing, but I believe doing it in camera creates more natural photographic results and saves a lot of time too.