I'm no expert on this topic but I have had to spend many hours correcting the wrong WB setting. (Even in RAW.) With that experience under my belt, I would say use a good white card.
I just ordered my Whi-Bal card a few weeks ago. It works great. Many of the options presented in this thread will work just fine. I got the Whi-Bal w/ a lanyard to carry around my neck. This way I KNOW I will always have what I need when I need it.
Post processing in CS2 is literally just a click. If so called "precise" color is important to you, I would make sure to use a Gretag or the Whi-bal. There is a lot of variance in what our eyes consider to be white. Having a standard means more consistent color.
geneluck, It's not as critical to preset WB if you are shooting RAW. But in some cases, changing the WB in post prod. can cause one of the RGB channels to clip. If you are already dealing with constraining factors like high ISO or high dynamic range, you COULD adversely affect image quality.
"HE began before the beginning had begun to begin."