What’s the Best Piece of Biotech from a Sci-Fi book?

There is some truly fantastic biotech in science fiction novels, some more likely than others, and some more useful. In this case, let's define biotech as any biotechnology that has modified humans, or another species to soup them up to anything more than they were when they were born, for example, a fancy eyeball, extra appendages or replaced appendages, brain implants, a productivity drug etc. Sometimes biotech books fit into a more cyberpunk or “biopunk” scene. So, here's the question, what single piece of biotech from a sci-fi book or novel series would you most like to have? It could be biotech from a human, humanoid, or completely different species. Vote for one of the selections below, or nominate your own preference by adding it into the poll. You can also check out what folks are nominating in the poll on Facebook here.