Lost is the only television series that I've ever gone to the trouble of buying the soundtrack CDs, and I'm looking forward to putting more of Michael Giacchino's beautiful work on my iPod. And Season 5 had some of the best music of the show's run. What I'm eager for most: getting that theme that we first heard during the Lamppost scene in "The Lie", and what most fans are calling "Jacob's Theme" that was introduced in "The Incident, Part 1".
(Incidentally Mr. Giacchino, if you ever read this: I would love to have a bunch of the score from "Happily Ever After" on the Season 6 soundtrack when it comes out next year. Especially everything from Desmond and Daniel's dialogue on through the end when Desmond asks for the manifest :-)