Off the top of my head my favorite soundtrack would have to be:
It probably has a lot to do with how well the music meshed with the movie. The soundtrack in and of itself is good, don't get me wrong, but had I not seen the movie (which was fuckin great) I might not be so fond of it.
anything by goblin, suspiria, tenebrae etc.
the crow soundtrack
SuperFly
the blade runner score is awesome.
and as previously mentioned Friday and Tales From the Hood (for the spice one track alone!)