From the archives: What's your best paper?

A while back I did a post talking about what I think is my best paper, and inviting readers to share their stories of their best papers. I thought it would attract a bazillion comments, but the only response was from an old friend of mine. But since so many of you were keen to share your stories of eating your study organisms and doing crazy things in the name of science, I figured I'd give you another chance to toot your own horns.

So tell us: what's your best paper (or your favorite paper, or the paper you're proudest of)? Why?