Episode: Season 5, Episode 24
What happens: George enlists in the Army by the end of season five. When he leaves the hospital, he saves a woman from getting run over by a bus, only to get hit himself. His colleagues don't immediately realise that it's him because he's mangled beyond recognition. Only when he uses his fingers to trace "007" onto Meredith's palm does she realise it's him. He and Izzie flatline at the same time, and we see the two of them walk into an lift, Izzie in her season two prom dress and George in an Army uniform. This is Grey's at its finest emotional hour.