The Long Goodbye (1973, R)

This is a film about the iconic private detective Phillip Marlow.  It's rated R, but a pretty soft one.  In most aspects I would peg it as more of a PG-13: some language but not very often, a couple scenes with violence but very little blood and very short in duration, but there were quite a few boobies (Marlowe's neighbors are hippie chicks and are one of the lighthearted humor aspects of the film).  Marlowe is played by Elliot Gould (MASH, Ocean's Eleven [and 12 and 13], American History X), who I still think of as the dad from The Big Hit.  Also, a young Arnold Schwarzenegger has a short appearance as mob muscle (you can identify him because he looks like he just ate two other wiseguys), and Henry Gibson (the head Chicago Neo-Nazi from The Blues Brothers) plays a doctor at a clinic.

One aspect of the film that I thought was kind of a problem was that so much of the dialogue (particularly Marlowe's muttered one-liners) were so soft in timbre that if, for example, you're trying to eat chips and guacamole as I was, you won't hear it and need to rewind.  The remarks sounded different compared to much of the rest of the audio and I'll bet it was dubbed in afterwards because it wouldn't pick up on the microphone when filming.  This hurts because his constant flippant remarks are a huge aspect of Marlowe's charm.  That along with his loyalty to his friends and his lack of concern over his health (which is occasionally represented by his choice of who to mouth off with).  Like many a good detective story, it has a broad cast of characters that the PI meets as he follows circumstance toward an answer: mobsters, doctors, police, socialites, writers and general crime lowlifes.  My favorite part of the film is that it hits every note that a detective movie should (it's not noir, because the shadows, graft and color scheme don't quite comply, but it's still pretty close to that level).  This is basically the template that many good stories will emulate. 
If you're a fan of private detective stories (example: George Stark's Parker novels or the Payback film, The Dresden Files [the first book is all I can speak to]) then you should watch this movie (I also highly recommend Brick, which is a sort of private detective story in which all of the characters are high school students; shockingly good film).  It's kind of like The Big Lebowski minus the Winnie The Pooh quirks.  For me it's a 4 star movie.