If you had too pick four... which four would you pick?

Ok. I am watching Star Trek for funsies again and I love it even more now than I did years ago. I'm a scifi addict!!

So I was having a discussion with a friend, and he asked, "If you had to pick four Star Trek The Original Series episodes, which would you pick?"

So here are mine:
Season 2; Measure of a Man
Season 5; The Inner Light (that whistle tune is just so... peaceful)
Season 6; Tapestry
Season ALL; anything with Q in it.

And what are yours?