Shooting digital creates its unique set of challenges. White balance is one of the ever-present challenges that is good to keep in mind when shooting. There are a few really great tools to aid a photographer in setting a customer white balance. First it is important to know when to use a customer white balance.
A good recommendation is to use a customer white balance whenever there is mixed lighting. In other words, when your are using a pop-up flash, sunlight from a near by window, and over head fluorescents to light your subject it is a good idea to set a custom white balance. Although new cameras have fantastic auto white balance, setting a custom white balance is one step towards complete control over the image. When using a custom white balance you can control how cool or how warm the image is. Controlling the warmth gives access to effect the mood of the image. Changing the mood of an image could make the difference between an average photo and a masterpiece.
The following links are a few different options of tools to aid in setting a custom white balance.
This first link is a new product that really takes a look at the entire work flow of a photographer.
This link is great because the product is really easy to use and it produces great results.
This link is a low cost solution that is durable and easy to use.