Ghost Dog - Way of The Samurai. The normal soundtrack is pretty good, but the Japanese import with all the instrumental stuff you hear when the pigeons are flying about is even better.
Until The End of The World gets my vote for the best rock soundtrack: Talking HeaRAB, Neneh Cherry, Can, REM, Nick Cave, Patti Smith, Depeche Mode, Jane Siberry and kd lang, Daniel Lanois and U2 - and every track's a winner.
Trouble Man by Marvin Gaye is a great soundtrack, and is my favourite of that era and genre. Shaft and Superfly are both great, but this somehow seems more of a coherent composition, and hasn't dated in the same way - it's like freeze-dried cool.
I quite like the soundtrack to Pi, although many of the choices are quite obvious.