A similar question got valuable answers just a few months ago: http://typophile.com/node/114656
I'm typesetting a text for a friend: a translation of a Latin text which has quite a few large notes in Classical Greek. I'm thinking about buying Garamond Premier Pro (which I've used before and really like), but first I wanted to see if someone here has other suggestions of nice serif fonts with a good polytonic Greek character set.