25th Hour was great. I fully agree that it is Spike Lee's best movie.
The Prestige - sure.
History of Violence - yes. Great movie, I thought.
Didn't see A Scanner Darkly or Stardust.
Master and Commander, meh.
Didn't see Grindhouse, yet. I need to fix that ASAP.
Kiss, Kiss, Bang, Bang was a fantastic movie and almost no one has seen it.
Watchmen was good, I enjoyed it. I'm not sure it's underrated, though.
Have not seen Me Without You, either.
Others from this thread:
Seven Psychopaths is fantastic. Probably Sam Rockwell's best performance and that, alone, is worth watching the movie. Plus, Christopher Walken.
I actually really like Must Love Dogs.
I also really like Thank You For Smoking.