On Sunday, Washington's Ryan Zimmerman hit a one-out, two-run homer off of the Yankees' Chien-Ming Wang to give the Nats a 3-2 win. What was even more unusual about this was that Wang was working on a complete game. I don't know how often in this era that a starter loses a complete game on a walkoff homer.
According to the story on MLB.com, the last time a National/Expo player to hit a walkoff homer was Orlando Cabrera on June 20, 2004 in Montreal. Cabrera's homer gave the Expos a 4-2 win over the White Sox. The losing pitcher that day was the White Sox starter, Jon Garland, who had gone the distance and allowed just three hits in the game.