1. Taxi Driver
My favourite movie of all time. The first film I ever saw that captured the dirtier side of nightlife. Basically what RadicalThrasher said, sleazy stuff that makes you wanna take a shower. Also might feature possibly the greatest example of a director doing a scene in their own film.
2. In the Realm of the Senses
Art film meets erotic thriller, based on a real life bizarre story of a 1930's geisha who was also a sadomasochist. Director Nagisa Oshima managed to both include unsimulated sex scenes
and make the film one of the most beautiful tales of romance ever created. Speaks to me on many levels.
3. Assault on Precinct 13
I love the build up with this one and it's a perfect example of Carpenter's music adding a whole other dimension of awesome to his films. Pretty insane violence for a 70's action film.
4. The Enforcer (Dirty Harry 3)
A right-wing feminist film, imagine that. Car chases in movies are cool but this one has one of the most epic on-foot chase sequences ever, complete with a sizzling jazz score. Bonus points for not reducing Harry's female partner to a vehicle for a cheap love interest.
5. The Omen
Classic satanic horror film where the supporting cast's performances were very essential in order to allow the leading child actor to give a very minimalist performance. That kid seemed so evil when I first watched The Omen haha. Also I love Gregory Peck.
6. Mad Dog Morgan
In many ways this movie encompasses the sheer insanity of the low/lower budget 70's film movement. Tons of drugs, booze, script rewrites, improvisation, controversy, dodgy looking wigs and fake beards, wacky fake accents, violence, further obfuscation of historical figures into mythical characters, the worshiping of the antihero and the outlaw and really dangerous looking stunts done cheaply and by amateurs.
Same director who made the notorious third Howling film featuring this legend and top tier actor, Burnham Burnham.
7. Carrie
The quintessential anti-bullying film? Apparently the book is one of the most frequently banned books in U.S. schools.
8. The Outlaw Josey Wales
Eastwood directed this one himself and it's a classic outlaw revenge western, but probably darker than most I would say and with some anti-war undertones. I think it's pretty weird that this film made tons of money and in the 90's was preserved for cultural relevance yet I never seem to hear people talking about it...
9. Marathon Man
Pauline Kael called it a "Jewish revenge fantasy" and though I don't think she meant that in a positive sense, it does have some merit. A pretty frantic film dripping with paranoia and desperation and featuring one of Hoffman's best ever performances which makes up for any of the film's shortcomings.
10. Bloodsucking Freaks
Purely trash cinema that only appeals to the dregs of society, basically a masterpiece of smut, sadism and sleaze. Even the detective is a piece of shit in this movie.
I'm happy with my list so far, if anything from my 'to watch' list blows my mind I'll alter it, but other than that I'll stick with these. Really looking forward to everybody else's lists though.