Den of Geeks has been compiling lists of underappreciated films through the years. Today they posted their list for 2006. They placed A Scanner Darkly at the very top. The film opened on July 6, 2006. Its opening weekend it made $391,672 playing on 17 screens for a screen average of $23,039.
You can checkout the entire list, as well as others, here. There were some films on the list that never made it onto my radar screen that sound like they may be worth a watch.