One of my favourite tracks would be, 'Oceanic 815'. It is really nice and calming then at the end it goes all creepy and LOSTified. Then it builds to a cliffhanger kind of feel, then we get the good old 'LOST' end of episode sound at the end.lol Reminds me of so many great episodes with cliffhangers and that things are not all what they seem ;-)
Here is a link to listen, also there are all the other tracks:
http://www.youtube.com/watch?v=5Nt-YMnwBoQ