
Doing over the day, this is not a new plot device, in fact it is the entire premise of Bill Murray's Ground Hog Day. Where he keeps doing the same day over and over again until he gets the girl, learns his lesson, and becomes a better man. So for a change of pace, I though I would highlight some great Groundhog Day episodes from Science Fiction Shows.
More after the jump.
Buffy the Vampire Slayer-Episode 105: Life Serial

Star Trek TNG-- Season 5, Episode 18,Cause and Effect

Stargate SG-1--Season 4, Episode 6 Window of Opportunity

The X-Files- Season 6, Episode 15, “Monday”

Angel--Season 5 Episode 19--Time Bomb

Title Text.

Superman Honorable mention

First, in Season 4, Episode 11 of Lois and Clark, entled, "'Twas the Night Before Mxyma," Christmas Eve is happening over and over again, and the people of Metropolis begin losing hope. Can Lois and Clark stop an imp from the "Fifth Dimension," best known as "Mr. Mxyzptlk," before it's too late and hope is gone forever?
The episode can be watched in its entirety here.
Then in Smallville's 100th episode, "Reckoning," Clark is finally willing to reveal his secret to Lana, but there are consequences. Jonathan and Lex learn the results of the senatorial election and the life of someone Clark loves - Lana - is finally taken away from him. A desperate Clark appeals to Jor-El for help, only to find himself frantically trying to save her again. Lionel reveals to Jonathan he has a little more up his sleeve. Minutes later, Jonathan dies of a heart attack in front of Martha and Clark.

What is your favorite time loop episode.