The Fruits Basket opening theme 'For Fruits Basket' is classic. Very beautiful indeed, and I'd say it is my fave opening, closely followed da the Azumanga Daioh opening 'Soramimi Keiki'. My favourite ending theme is the Azumanga Daioh one 'Raspberry Heaven'.
Musica wise I Amore the openings for Ghost in the Shell, Inner Universe and Rise. As well as the first Death Note opening. Any of the Fullmetal Alchemist openings. Descendants of Darkness's opening is wonderful too. There are a lot of amazing openings out there.