Check out www.soundtrack.net for answers to questions like this. According to their page on Black Hawk Down Black Hawk Down Trailer Music
The music is as follows:
"Natural Blues" - Moby
"Sarabande, Harpsichord Suite in D Minor" - Georg Friedrich Handel
"Why Does My Heart Feel So Bad" - Moby
"Knocking on Heaven's Door" - Bob Dylan
Gladiator (2000) - Hans Zimmer
"The Space Between" - Dave Matthews Band
And a pop over to cdnow.com for soundclips leads to "Why Does My Heart Feel So Bad" as the song that is playing when the helicopter crashes.
I hope this helps!