David Bowie will always live in my memory as his character Jareth, the Goblin King, in the 1986 Jim Henson movie Labyrinth. The film was written by Terry Jones of Monty Python and largely designed by Brian Froud, a rather strange fiction writer and artist who literally believes in most of the faeries and other strange creatures he paints and brings to life in film.
Bowie was a sinister and ultra-cool villain, the god-like master of this realistic fantasy world. As well as starring, Bowie contributed extensively to the soundtrack, writing some of the songs and singing at least a little on all of them.
More recently Bowie has contributed works to two other soundtracks: 1997's The Saint and 2003's Underworld, as well as collaborating with Nine Inch Nails for "I'm Afraid of Americans".
His track on The Saint soundtrack, "Dead Man Walking," is a poppy techno song, which fits in with the rest of the album. Bowie, though, uses strange operatic singing samples and a driving melody to make his music more palatable and interesting then your average rave music. The lyrics are better, too. I particularly like the line "And I'm gone, like I'm dancing on angels, and I'm gone . . . through the crack in the past."
For Underworld Bowie did a song called "Bring me the Disco King," featuring Maynard James Keenan (of Tool and A Perfect Circle), actress/singer Milla Jovovich, and John Frusciante (guitarist for The Red Hot Chili Peppers). All the singers contribute powerful and dark performances, and the accompaniment consists only of one otherworldly guitar riff and a powerful chorus of strings. One of the best songs of all time.