I don't think I can claim any one song for a theme, but I LOVE soundtracks and movie scores.
Dances with Wolves
Rainman
The Commitments
Top Gun
Footloose
Born on the Fourth of July
The Color Purple
Witness (I would love getting that on CD)
Lord of the Rings
Natural Born Killers (the Leonard Cohen stuff was great in that)
That's my ten. Rainman has some great tunes on its soundtrack, inlcuding Etta James' "At Last", and Hans Zimmer's scoring is unreal. I used some if it for my college video projects as background music.
Good music from an otherwise horrible movie. BTW, Leonard Cohen also did some great music for a recent Nick Nolte flick THE GOOD THIEF.