- Back to the Future Trilogy - a great adventure/comedy series. I love all three of them. Back to the Future Part II is the highlight.
- Die Hard Trilogy - Each of the three are awesome. The first one is the highlight of the series but the second and third are almost as good.
- Lethal Weapon Quadrilogy - Mel Gibson and Danny Glover are a great on-screen team. And with each movie they add even stars like Joe Pesci, Rene Russo, Chris Rock and Jet Li. To be honest I found Lethal Weapon 4 to be the best but I'm in the minority.
- Star Wars Original Trilogy - Great movies. Highlight is the Empire Strikes Back with Return of the Jedi not far behind.
- The Terminator Trilogy - I loved all three of them but the second was definitely the best.
Honorable Mention
Beverly Hills Cop Trilogy - a very underrated Trilogy. Everyone loved the first one, many viewed the second as a disappointment and almost everyone hates the third one. I love them all. Axel Foley is awesome!
Lord of the Rings Trilogy - Great movies. The Extended versions are even better. I enjoyed the Fellowship the most because that was when the whole cast was completely together.
Indiana Jones Trilogy - I'm not as big of an Indiana Jones fan as most but I still love these movies. I really can't pick a favorite out of the three.
Alien Quadrilogy - I really enjoyed the first two but I really didn't care much for Alien 3 but Alien: Resurrection was ok but nothing special.
American Pie Trilogy - great comedies that don't seem to be too popular around here. I though the second was the best.
Austin Powers Trilogy - Second was the best. It seemed the third one was very unoriginal and recycled jokes from the first two but a good trilogy nonetheless.
Rambo Trilogy - First Blood was an great movie. Rambo II was ok but I really liked the third one regardless of what most people think.
Crocodile Dundee Trilogy - some of you might be surprised to see this here but the first two were movies I loved as a kid, while the third actually wasn't too bad. Most people never gave it a chance.
Jurassic Park Trilogy - I loved the first one as everyone did. I even really liked the second one which most people did not like. The third was solid but unnecessary.
Rocky series (Quintilogy? haha) - I actually like all 5 but the first is clearly the best with each movie getting a little worse from that point on.
Batman Quadrilogy - the first two were great, while the last two were kind of lame but not as terrible as a lot of people think.
Superman Quadrilogy - the first two are kind of classics. Like the Batman movies, the last two were pretty bad.
The Naked Gun Trilogy - love these movies. I'm in the minority but I actually like 2 1/2 and 33 1/3 the best of the three.
Star Wars Prequel Trilogy - nowhere near as good as the original trilogy but still kind of underrated I think. I really enjoyed Episode 3.
Matrix Trilogy - I really liked the first one but not as much as most people. I loved the action in Reloaded but was still disappointed. Revolutions was just pure garbage. It was terrible.
Evil Dead Trilogy - the first two were great. For years I had seen Army of Darkness not knowing it was the third part of a trilogy and I liked the movie. Evil Dead 1 and 2 were even better.
Romero's Dead Trilogy - I have only seen Night and Dawn but I play to see Day before Land of the Dead comes out next month.
RoboCop Trilogy - first movie was pretty good. The second was somewhat entertaining although lame. The third was just a joke.
Karate Kid Quadrilogy - nothing spectacular but 80's classics.
Major League Trilogy - probably a surprise to most but I loved the first two when I was younger. The third was kind of stupid but oh well.