#2. "RE: Digital White Balance Cards or 18% Grey Cards" In response to In response to 1
Fountain Inn, US
This is a well discussed topic and there are as many opinions about it as there are photographers.
I will here offer mine.
The only time you will need scientifically perfect white balance is when you do that shoot for a paint company or fabric company who will demand EXACT matches to their pride and joy colors. Otherwise it's quite subjective on your part. What looks right to you.
Use anything white at the site. There is always something. I use napkins, a white tee shirt, a table cloth, anything white. Shoot a WB preset of the item then shoot away using that preset. IF you're at a wedding for instance that takes place in more than one room with differing lighting, create a preset in each room and save it, then remember to change it when you move from room to room. You do NOT need a spectrally, scientifically balanced, camera branded (and therefor expensive) product.
Better than that, simply use auto white balance, shoot everything in RAW, making sure to shoot something white in each environment, then in post processing, do a white balance grey-point adjustment on that photo in each group and do a batch process on all the rest. Then you don't have to deal with it at the shoot.