I've not seen the movie Once yet as I don't think it ever played anywhere near me, but I've heard bits and pieces of the plot line. Glen Hansard (of The Frames) is "the guy." Markéta Irglová is "the girl." Their paths cross on the streets of Dublin, and fate steps in to make their paths cross. He's a street musician and she's as struggling single mom, and the music they make brings them together.
The movie was produced by John Carney, who played bass for The Frames from 1991 to 1993 (hence the Hansard connection). The soundtrack is simply dynamite original music, and from what I hear, plays a major part in the plot development. Frames fans will recognize Hansard's vocalistic stylings on these moving pieces. Along with music newcomer Markéta Irglová, the duo released The Swell Season last year, from which four tracks appear on this soundtrack, along with nine additional tracks (one of which is from the band Interference - anyone know anything about them?).
Give the pair a listen, if you haven't already. Below is a track from Glen and Marketa (in which you get a wonderful listen of her hauntingly beautiful voice) as well as a rather cheeky one from just Glen. And of course, how could I not include one from the Frames?
Glen Hansard & Markéta Irglová - If You Want Me : Once Soundtrack
Glen Hansard - Broken Hearted Hoover Fixer Sucker Guy : Once Soundtrack
The Frames - Star Star/Pure Imagination (live Medley) : Set List