@strawCake - The outer cell member stuck in my head too when I took biology. A cell in the human body couldn't function without its outer membrane, after all. I distinctly remember being really fascinated by the channel proteins in the membrane too. They were shaped a certain way that only some compounds could pass through the proteins and get inside of the cell.
I also thought the nucleus was pretty cool. After all, it holds the DNA, which controls everything the cell (and by extension the whole human body) does.