Hmm well I have quite a comprehensive list of "best songs" but to be perfectly honest it changes as often as the wind with me...However for quite some time now FFIX's "Bran Bal" theme has been my most treasured.
Others include everyones favourite "Fishermans Horizon" (FFVIII), "One Winged Angel" (FFVII), "Cids Theme" (FFVII), Almost all the FFVI OST blah blah Final Fantasy....
Non FF, hmm i'd say some of the Suikoden 1 stuff was superb, though having not played it for 5 years or seen an available OST OR even a downloadable mp3, I cant name a particular track.