Best Scene Ever
If you haven't watched Lost and are planning on watching it, then do not watch the following scene. It's a spoiler and it's from the season 5 finale, "The Incident." The scene is so emotional and important.
Here's a less spoiler-filled favorite scene.. the beginning of Desperate Housewives. It's stumbled a bit recently, but it would be very hard to regain the magic of this opening scene for anyone.