Here’s a replacement lens cap that purports to help you set the perfect white balance on your DSLR every time, without carrying around a gray card. Interesting idea and tempting, sure, but the $45 price tag (at the low end) has me thinking up some home-grown alternatives — a spare lens cap and a piece of milk jug, perhaps?

Psuedo-update: Amazon carries several cheaper versions of the same idea. Cheap enough that a ghetto hack might not even be worth it.