Get Over You by The Undertones. Way back in the day, this was the song that made me want to be in a band. Everything that was good and righteous about punk rock and pop music is wrapped up in one wonderful little package of guitar, drums, and warbling teen angst. There are a number of Undertones songs that meet this criteria but this one is, well, perfect.
Please note that this dates from the era prior to Feargal Sharkey completely sucking.