I know what you mean--"eargasmic" lol is a good description ;)
I can't think of many songs with piano in them at the moment, these stand out though:
Haru Haru- Big Bang
Because of You- After School
Love In The Ice- DBSK (Japanese)
~(I'll come back again to edit if I remember some more songs that have piano parts in them)..
edit: Ah! I just thought of some more! ^__^
Living in the Heart- Untouchable (ft. Narsha -from Brown Eyed Girls)
Um, if you like slow songs with piano accompaniment then you might like these (they're not upbeat, it's more melodic):
Can't Let You Go Even If I Die- 2AM
Without Words- 9th Street
My Everything- Lee Min Ho
I'm sure there's quite a few other songs out there too..
(I might edit again.. =__=;; sorry!)
re-edit: The other answerers gave really good suggestions, so I couldn't find anything else..
Hope you'll have lots of eargasms lol xD