Six Feet Under was great. Like The Sopranos, it was one of the first (mainstream) shows I remember that treated television drama as a mature, cinematic artform.
I have a feeling that it's aged pretty badly though, at least in comparison to some of the shows that's come since. I remember it moving at a deathly (har har) slow pace, and being too introspective for its own good while not much happens. It's more about character study and atmosphere I guess, and it does do both of those things well. Very well.
Plus it was the birth of the Narm