For Monkey Island in general, "Gone" by Tokyo Police Club seems to fit in tone:
http://www.youtube.com/watch?v=mP9Nh2q6OUM
TOMI Chapter 4, The Police, "Bring on the Night"
-Kinda for the sense of uncertainty and a certain desire for closure on Guybrush's part (Though it happens with disastrous consequences)
http://www.youtube.com/watch?v=Bz1mEMiNPHQ
TOMI Chapter 5, Rush, "Ghost Rider"
-A bit risky I know, but the sense of continuing to find hope even through the bleakest darkness seems to work well with the various demons (Both physical and emotional) that Guybrush has to grapple with in this chapter.
http://www.youtube.com/watch?v=cukCx...eature=related
Anyhoo, lemme know what you think.