To follow up the Bad Movies topic, what are some folks most underrated movies...One of my more underrated moves is
True Romance - classic cast..though some have definately gone downhill.. some classic scenes (Dennis Hopper and Christopher Walken)...
Tony Soprano before his time....
Others?


Well, considering they are my two favorite films of all time, I don't think Michael Mann's Heat and Luc Besson's Leon can be highly rated enough.
To answer your question more directly, I would say one of two John Carpenter films: The Thing (1982), which is critically acclaimed but never mentioned in the discussion of Best Horror Film Ever (as I think it should be), and Assault on Precinct 13 (1976), which is just awesome and underrated by any definition.