What are your favourite time-loop based books, movies and video games?

I absolutely love the premise of a time-loop. I find them fascinating, and there are so many variations to explore. Inevitably, I find myself fantasizing about waking up in my own younger body and the shenanigans I would get up to with so much future knowledge (before existential dread of meeting the same people and creating the same family kick in).

• Short time-loops where someone relives the same day, or an even shorter period.
• Medium time-loops where someone can live days, weeks, months or even years before resetting - often when they die.
• Longer time-loops where someone effectively relives an entire human lifespan on repeat.
• Shared time-loops where other people are independently looping - a great source of conflict.

And plenty more besides.

I'll share some of my favourite examples in a comment, but please share your favourites and tell us why you love them.