Neighbourhood #1 (Tunnels) by The Arcade Fire.
This was one of the songs that joyed me up enough to get through January through April 2006, when I was mourning two really big losses at the same time. I'd come to work early (I had them on the work computer), play them in the staff room before the other teachers showed up to begin the day of preschool. It was either this one, the end of Beethoven's 9th (which I described earlier), or Thunder Road, by Bruce Springsteen, which is so good I'll forgive every saxophone solo he's recorded in his entire career (saxophone solos and synthesizers are the two things I hate most about '80s music). Without these to start my day, I have no idea where I'd be right now.