What are the "must see" post-apocalyptic movies?

I didn't answer when I first saw this thread because I spent far too long trying to decide what I thought were important movies for a PA fan to see. I think I have my list sorted now and it's way longer than it probably should be, but I think all of these movies should be seen (I've left out movies I haven't seen).
As much as it's based on movies I personally liked, it's also based on what has been influential and on the different approaches taken by the movies themselves to tell their stories.

Post-Apocalyptic: -
Threads (as mentioned, a harsh, uncompromising view of the aftermath of total nuclear war - made to scare the 'nuclear war good feelings' out of people)
Mad Max + Mad Max 2 (should be seen together to make a 2 part story even though Mad Max is apocalyptic while Mad Max 2 is post-apocalyptic)
The Quiet Earth (what would you do if you were the last person alive and you thought it was all your fault?)
Damnation Alley (yeah it was a cheesy take on the novel but still it is kinda cool... well, almost...)
Delicatessen (a French black comedy about a butcher who runs an apartment block and tries to keep his tenants alive)
A Boy And His Dog (a young man and a dog search the wastes for food and sex - a trippy movie in places, I'm sure the underground society was the basis for the RPG Paranoia)
Hardware AKA Mark 13 (I love this movie, it was like a cross between The Terminator and the 2000AD comics - it was inspired by a 2000AD story so that's no surprise)
The Last Man On Earth (a somewhat dated movie treatment of the novel I Am Legend but better than The Omega Man and vastly superior to the action movie shtick that Will Smith applied to the story)
Le Dernier Combat AKA The Last Battle (another French movie, set in a desert wasteland where people have stopped talking and do what you might, nothing really changes, only your place in them does - I also picked this one because it's very different to most of the movies on my list)
On The Beach (the crew of a US sub finds very temporary shelter in Australia after a nuclear war, examines the thoughts of people as they confront the end of humanity)
Tank Girl (it's a bit of fun to counterbalance the usual doom & gloom of the PA world, plus it has evil corporations controlling the stuff of life itself)
Final Fantasy: The Spirits Within (CGI movie, alien 'phantoms' have devastated the Earth, a military officer wants to end the threat but it means destroying the planet)
Silent Running (all the plant life on Earth has been made extinct, only a fleet of spaceships keeps any plantlife alive, until the order is given to discard the greenhouse domes from the ships)
Logan's Run (society is maintained in domed cities to prevent the overuse of allegedly scant natural resources, to do this, every citizen must die upon reaching 30 years of age, some refuse to accept their fate)
Gunhed (a Japanese live-action mecha film wherein a rogue AI is happily plotting the destruction of humanity, a group of scavengers and a Texas Air Ranger are all that stand in it's way)
THX 1138 (I include this because although it's dystopian and it isn't specifically stated, it appears that humanity has been driven into underground cities by some cataclysm on the surface of the planet)

Apocalyptic: -
Day The World Ended (yeah this is a really bad Roger Corman flick but it's based on the fears and lack of knowledge about nuclear war that the public had in the 1950s - sort of a "see this because this is what they thought back then" thing).
The Road (what would you do to save your child when the world around you is starving to death?)
This Is Not A Test (another US 1950s-60s movie dealing with the fears of the public towards nuclear war, not a great movie but still interesting - a group get stranded on a stretch of highway when war is declared and they must all come to terms with not just the war, but what they're willing to do to survive)
Dr Strangelove: or How I Learned To Stop Worrying And Love The Bomb (another black comedy, this time a satire on the nuclear arms race, there's a number of great scenes and dialogue such as one of my personal favs "You can't fight in here, this is the war room!")
Children Of Men (another look at how we would handle the end of our species)
Babylon AD (in a world plagued by economic collapse and rampant warfare, a cynical mercenary has to deliver a potential messiah to a religious group that's more corporate than pious)
When Worlds Collide (a 1950s movie about a planetary impact event that will doom all life on Earth, a lifeboat is available but fights ensue over who will be saved)
Invasion of the Body Snatchers - 1978 version (an alien world is doomed, to survive the aliens subvert humans so that they can live on Earth - something of a commentary on the 1970s obsession with the wants of the individual over the needs of society)
Voyage To the Bottom Of the Sea (1960s movie about a research sub that is the only thing able to prevent the Van Allen radiation belt, now on fire, from overheating the Earth and destroying life on the planet)
The Terminator franchise up to number 3 (probably did more to put the fear or robots into people than any other movie but still leaves them feeling they might get out of their self-inflicted predicament... or will they...)
Them! (another 1950s 'fear the mad scientists and the atomic bomb' movie, this one featuring giant ants but it's kinda cool for the suspense - you don't even see the ants until about halfway into the movie - and to see 1950s Los Angeles including going into the storm drain system)