Harbor Themes by Jesper Kyd. Awesome music from an awesome game. And if you'd like to hear it in crystal clear sound, a.k.a. the way it was meant to be heard, buy the CD:
http://www.amazon.com/Hitman-Codename-47-Silent-Assassin/dp/B000A2GP5W
Edit: The song ends after 06:50, some youtube glitch decided to add four extra minutes of silence due to the song's awesomeness.
