Glen Murray to Palace. Brighton had just been promoted and had a bit of money to spend, so they let their star man leave for Palace, a team who at the time had very little to spend and were seen as relegation fodder, a season later he's scoring for fun, 2 more today against Brighton.
He left on a free I believe. I agree what you're saying though, at the time it seemed a strange one, leaving for your current club's rivals who were battling against relegation at the time. I'm sure he got a decent signing on fee for his move though, and at the minute, it's looking like he made a very good move.