I nominate Barton Fink

It's not often I shamelessly lift links from Metafilter, and I draw some affirmation from that fact in doing it this time:
The 100 most overlooked films of the 1990s? Some atrocities are included (although precisely which ones to categorise as 'atrocities' is a controversial matter, it would seem) but there are some films well worth seeking out. Glengarry Glen Ross may be most deserving in the sense that almost no one seems to have heard of it, but it's very good (although perhaps a little harrowing in its accuracy for those of us who know what cold-calling sales feels like).