This song was released both by The Frames on The Cost album and Glen Hansard’s side project called the Swell Season with Marketa Irglova. It was featured on the movie Once which I really, really liked. You can get the lyrics and listen to the song (along with a video of clips of the movie) here.

Intro & Verses  

   C               F               C               F
e ---------0---------------1---0-----------0------------------------------
B -1---3-------3---1---3-----------1---3-------0---1---1---1---1----------
G ---0---0---0---0---2---2---2---2---0---0---0---0---2---2---2---2--------
D -----------------3-------------------------------3----------------------
A -3-------------------------------3--------------------------------------
E ------------------------------------------------------------------------  

Verses: C - F - C - F (tab above)
Pre-Chorus chords: Am - G - F - G - Am - G - F
Chorus chords: C - F - Am - F

Update (1.8.08): After promising in the comments to get around to the tab
for the pre-chorus section, here's how I play it. Not really sure if it's
even close to how Glen plays it but it works alright methinks. If you have
a better version, let me know:

   Am      G       F       G       Am      G       F
e -----0---------------0---------------0-------0--------------------------
B -1-------1---0-1-1-------1---0-1-1-------1-------1---1-1----------------
G ---2---2---2-------2---2---2-------2---2---2---2-0h2-2-2----etc.--------
D -----------------3-------------------------------3---3-3----------------
A -0-------------------------------0--------------------------------------
E ---------3---------------3---------------3------------------------------