I was just watching The Truman Show on TV and realized that I actually wanted to see a sequel to this film so
Which films that not yet have a sequel actually deserves a sequel?

The Incredibles
Freaky Friday

basically in any film where the characters are so successful that we would be thrilled to see them again and again...

Some movies are better as stand-alones.

yes, for example predator or scary movie^^

Not quite about Predator though.