3. The Doctor's Wife
This one is Neil Gaiman, so it's full of scary moments. The overall concept seems like it could be carried out without scares, but the episode is full of spooky, creepy, chilling moments that make everything so much more awesome. My personal favorite is the reveal of the "patchwork people," which is such a freakishly logical thought, their internal organs and their limbs removed and patched back together. There's also the Ood that leads Amy on into tentacles, the increasingly aging and scary Rory, the House's takeover of the Tardis, and plenty more scattered here and there. The lights can be turned off within Amy's mind. The planet that is smaller on the inside does not like you, and will kill you for pure pleasure. And it can take over the safest place on the show, make it into a house of horrors: the Tardis itself. Sorry Mr. Gaiman, but this one was way scarier than "Nightmare in Silver."