Originally Posted by Kurt Wagner
There are plenty of great trilogies...
Star Wars Episodes 4-6
Back to the Future
The Bourne Trilogy
Lord of the Rings
I agree and don't agree with some of the listings above...
Godfather - third movie is considered significantly weaker than first 2; hardly escapes the 3rd act curse
Toy Story - yes, a truly fantastic trilogy that gets better with each movie
Star Wars - see Toy Story
Back to the Future - a good trilogy, but the sequels are notable steps down from the first.
Bourne - solid trilogy, gets better with each film
LOTR - perfect trilogy, but really just one long film split into three portions