One from my Visual Slushpile photo blog:
This mega-close-up shot of tiny buds on a tree branch (they're each smaller than a pea) revealed an even tinier white speck hanging in the air between them. One can just barely discern that it's clinging on one of two almost-invisible strands of web.
Is it a spider egg sac? Or an actual bit of fluffy detritus that floated along and got caught in a web?
My best guess is that it's a young specimen of those weird white insects that look like super-tiny bits of fluff even as adults. I tried a brief stab at googling and didn't see any immediate answers. Apparently a lot of people are in the same boat as me; they've seen it before but can't identify it.