It's impossible for me to pick a top 5. But I did write a blog 363 days ago in which I made 4 top-5 lists, to give you some ideas.
My favorite campy-but-epic sci-fi movies of each decade:
1960s: Barbarella
1970s: Logan's Run
1980s: Flash Gordon
1990s: The Fifth Element
2000s: X-Men: The Last Stand
(The 1980s is the only decade I had to think about. My definition of epic seems to lean towards saving the planet or civilization or the universe, so I couldn't count Back to the Future 2 or Brazil, but they get honorable mentions. And if you don't think the X-Men movie was campy, watch it again. He says "I'm the Juggernaut, bitch." And it's epic as balls.)
My favorite serious business sci-fi movies of each decade:
1960s: 2001: A Space Oddysey
1970s: Solyaris
1980s: Dune
1990s: Twelve Monkeys
2000s: Children of Men
(Frank Herbert, the author of the original 6 Dune novels was also the script consultant on Flash Gordon!)
My favorite 5 musicals of all time:
1. Happiness of the Katakuris
2. Forbidden Zone
3. Little Shop of Horrors (1986)
4. Labyrinth
5. Hair
My favorite 5 too-arty-for-your-mom movies of all time:
1. Week-End - by Godard
2. Takeshis' - by Kitano
3. Eraserhead - by Lynch
4. Un Chien Andalou - by Bunuel
5. 8 1/2 - by Fellini
