AWB works pretty well in the majority of cases (with normal light). If you shoot RAW then you gain extra WB control during post-processing. Of course it is always better to get it right on camera because you don't have to spend too much time on the computer later and because post-processing is limited and when you touch the White Balance in any software, even Aperture or Lightroom, you are also doing modifications to the colors. There's a great way to get that perfect white balance on your camera every time, it's the custom white balance feature that your camera has. To use it buy or print (but with your current printer problem I'd rather buy it) a Neutral Grey card, its cost shouldn't set you back more than a couple of quids. Carry that every where and use it to set the Custom WB and then use it until the light has changed considerably. You'll see the difference with sunsets and sunrises. There are more refined WB devices that achieve the same result like the ExpoDisc
with more precise results, but also much more expensive: $69.95 to $169.95. I'd say start with a neutral grey card and take it from there.