Boogie Nights
Paul Thomas Anderson's hilarous 1997 satire on the porn industry gave Mark Wahlberg a great role, briefly made us applaud Burt Reynolds again, and cemented Julianne Moore's status as an extremely powerful leading lady. Oh, and it featured Heather Graham naked.
With his bizarrely timid (and extremely homosexual) characterisation of porn crew member Scotty J, Hoffman broke through with this poignant portrayal, comfortably standing his own amid a very talented ensemble cast.
Hoffman has since prominently featured in the director's films, including Punch-Drunk Love and Magnolia.