I may be missing a couple, but if I am, I guarantee you that if I heard them playing, it would remind me of the Summer of '04. Similarly, I expect that I'll pick up a few songs on the radio here in Scotland that will remind me of my time in Aberdeen whenever I hear them for the rest of my life. I've picked up a couple of them thus far, so I figured I'd share them in case they're not destined to play on American radios. The first is "Boy" by Nina Nesbitt, who's actually from Edinburgh.
The second is "Disconnected" by Keane - somewhat comforting, given that Keane was one of the bands I discovered in 2004.
Of course, it's a touch disconcerting that both of these are break-up songs. Maybe I'll hear some other good music that's a bit less melancholy as the year continues.