My list(s) tend towards the "science fiction" region, and doesn't really include the "fantasy" section. obvious crossover issues there...

Movies:

• 50s-Invastion of the Body Snatchers, The Day the Earth Stood Still, War of the Worlds, Godzilla (54, not 56), When Worlds Collide
• 60s-2001, Planet of the Apes, Fantastic Voyage, The Time Machine, Marooned
• 70s-Star Wars, Close Encounters, A Clockwork Orange, Alien, Mad Max
• 80s-The Empire Strikes Back, Blade Runner, Terminator, Akira (I you limit yourself to 5 films, the 80s gets severely shortchanged. SO MUCH good stuff in the 80s. The golden age of sci fi film, for sure.)
• 90s-12 Monkeys, Jurassic Park, The Matrix, Stargate, Ghost in the Shell (In a weird, weird change, the 90s SUCKED for sci fi. largely bad sequels to great 80s movies)
• 00s-Pitch Black, Donnie Darko, Serenity, District 9, Moon
• 10s-Interstellar, Iron Sky, Pacific Rim, John Carter..(well, we have 5 more years to fill this list...)

Television (based on series starts. Some had their primary run in the next decade...)

*50s-Not a lot here-very early stuff, radio serial-type things. But Twilight Zone and World of Giants technically started in 1959... *60s-Star Trek, Doctor Who, Lost in Space, Outer Limits, Thunderbirds *70s-Battlestar Galactica, 6 Million Dollar Man, Space 1999, Buck Rogers, Star Trek Animated Series *80s-V, Voyagers, STNG, Red Dwarf, Quantum Leap *90s-Stargate SG1, X Files, Farscape, Babylon 5, The Outer Limits *00s-Firefly, Battlestar Galactica, Dark Angel, SW Clone Wars, Stargate Atlantis *10s-defiance, Orphan Black...wow sucks so far...

Books-

50s-The Demolished Man, Caves of Steel, Childhood's end, Foundation, Starship Troopers (Like 80s sci fi movies, the 50s were so full of seminal, must read stuff...too much for just 5!!) *60s-Flowers for Algernon, Dune, Lord of Light, Solaris, A Wrinkle in Time *70s-The Hitchhiker's Guide to the Galaxy, Gateway, Ringworld, Rendezvous with Rama, To Your Scattered Bodies Go *80s-Neuromancer, Ender's Game, Startide Rising, Blood Music, Hyperion *90s-Snow Crash, Red Mars, Beggars in Spain, The Reality Dysfunction, Raft *00s- The Windup Girl, (honestyl haven't read enough novels *from this decade to fill this with "essential" books) *10s-Ready Player One, (again haven't ready enough novels from this decade fill out 5)