Can't narrow it down to just one. Champagne supernova by Oasis is definitely up there, along with why does it always rain on me by Travis.
Champagne supernova is just a great song, and I found it (and overplayed it) in my first year of university when I was looking up old music from my childhood. The Travis one I rediscovered after hearing it on the radio one day a few years ago and recognising bits of it from when I was 3 or 4.
Quite a few other songs I really like are ones that bring up feelings of nostalgia. e.g. escape by Enrique Iglesias, yellow by Coldplay. Bruce Springsteen's Born in the USA album is up there as well - I used to go lots of places with my dad when I was a kid and he often played that sort of stuff in the car, so listening to it takes me back to that time.
More recently, I quite like a few Kodaline songs, like better, coming alive, and brand new day. There are others too, like gale song by the Lumineers.