i LOVE classical music. debussy would have to be my favorite- the "debussy for daydreaming" album (available on itunes) is the most calming music i know of. also really like tchaikovsky alot- around christmas time, i usually cant get enough of the nutcraker music. shostakovich is pretty great. i will second vivaldi's four seasons- great stuff.
i REALLY like a couple npr programs that play classical. performance today always has really good stuff which ive never heard of. and from the top is a cool show featuring young classical musicians.