Consider the Novoflex Zebra 2 Sided Grey Card, 18% Grey / White, 6 x 8 in. card from the accessory specialist Novoflex. Checking always has to beat guessing; and now there's a perfect check card for exposure metering and white balance.
The flexible check card, made of a special polymer, has an antireflection coating on both sides: one side white, the other grey. The grey side serves as reference area for exposure metering while the white side enables correct white balance that is so important in digital photography.
Handling couldn't be easier. The camera takes a light reading of either side of the check card to perform an exposure measurement or white balance and, hey presto, the camera is set optimally for the prevailing light conditions to guarantee perfect shots.
The Novoflex ZEBRA check card is a must for every quality-conscious photographer, regardless of the medium used to capture images.