I've been experimenting with this inexpensive white balance cap for the last three months. Recently used it on a week long project will lots of mixed lighting and it performed very well. I've only had it fail in one extremely difficult lighting situation.

Mennon White balance lens cap 72mm ($5.07) at Amazon.com

Simply compose your shot, hold the cap over your lens and perform manual white balance.

You may wish to purchase a size bigger than your largest lens.

Dan, I had read the Mennon caps tended to give a bluish cast. I bought a grey card today, but the cap would be easier, for sure.

I used to use white cards, but had mixed results. With these GH2s and the horrible auto white balance, I needed something. My photos and video camer out perfectly today, so happy. I am hooked on my grey card.

Anyway, I may order the Mennon if you recommend it. At $5 you can't go wrong.

Is the WB cap how you have setting the white balance for your outdoor stuff? Based on that it sure looks good.

BHPhoto sells some $5 microfiber cleaning cloths that happen to be 18% grey... Handy, plus they have a grippy side to help wrestle off recalcitrant filters and the like. I keep two in every camera bag.

Most times I dial in 3200 or use one of the daylight presets. Usually only manual wb if there are fluoros I can't kill.

Kevin, my problems, as I experienced on a shoot last week, was things were too red in the sun, and too cool in the shade.

I might have not had WB set properly, but I remember checking it. Things came out so weird, that yesterday I used the card everytime I moved, and it gave me confidence, as I cannot be sure with colors based on the LCD when I'm outdoors. To make matters worse, I have trouble with colors anyway.

You mentioned 18%, which is what my local store had available yesterday, I have but I've read that 10% is better for digital and that 18% is a throwback to film days, but I don't know.