"Sweet Disposition" - The Temper Trap.
Probably one of the latest arrivals to my chart, this initially came to my attention thanks to a 4 Music trailer: then something truly remarkable happened - this song made it into the UK top 20. I suppose you would call it a 'sleeper hit', which managed to stay in the chart for a while without much significant radio airplay.
This, I strongly suspect, is a band with a very bright future. Their first album may be patchy but shows immense promise of fabulous things to come: and their lead singer Dougy Mandagi has one amazing voice.