I really liked the song "Here's to you" during the credits of Metal Gear Solid 4: Guns of the Patriots. I felt it was very well used and suited for the game, considering the song's mood and theme and when you finish MGS4, you realise it's the end of the entire MGS saga (at least, with Solid Snake as the lead).
http://www.youtube.com/watch?v=7lAd9Fo8HgU
http://www.youtube.com/watch?v=7lAd9Fo8HgU