Famous names: The first film by Darren Aronofsky, who would go on to heretofore untold levels of squick with his followup, Requiem for a Dream.
Crunchy goodness: 5
Memorable product tie-in: Every techno DJ alive has the soundtrack.
Sights you'll never unsee: Drill plus cranium equals super happy mirror splatter!
Design breakthrough: Many pre-DV indie films were shot in black and white for budgetary reasons, but Pi's gorgeous, high-grain chiaroscuro cinematography is vital to the mood; though it's never mentioned in the dialogue, I've always suspected the character is color-blind, as it feels like we're seeing the world through his eyes.