It can be any genre, as long as it makes you feel absolutely joyful.
Cloud Smiles (embedded) is the first that comes to mind, and has the strongest effect on me. It just makes me cry of happiness..
Here are some others:
Frontier Village Dali IX, Final Fantasy IX.
Kiss, Byousoku 5 Centimeter (5 Centimeter Per Second)
1,000 Words, Final Fantasy X
Aerith's Theme, Final Fantasy VII
Descendant of Shinobi by Reuben Kee Got this from his site a long time ago, but it seems the links don't work anymore so I uploaded it.
Yes, I am quite into Final Fantasy soundtracks.