These covers bring an added sentimental touch to these songs. I especially found Bolero cover to be even more breathtaking than the original song.
BOLERO by dorismusik
You can download this cover on her video page here.
DON'T SAY GOODBYE (Mirotic Album) by dorismusik
MIROTIC by chibiyumiii
Do you guys have recent favourite you want to share?
Speaking of piano, an internationally acclaimed Korean pianist wanted to play a peice for DBSK! That would be quite an honor if it were to happen.
You may have heard of him -- Yiruma. (Alot of Twilight fans might know who I am talking about, especially if you had heard the popular fan-suggested unofficial Bella's lullaby on Youtube which, combining other similar videos, had well over 3 million hits! River Flows In You is a song composed and played by Yiruma!)

Over at Dnbn, a TVXQ fan posted an article which featured Yiruma and in the article he stated:
"I want to give a music piece to an idol group like TVXQ."
Yiruma is a world famous Korean pianist / composer. He's 30 years old, born in Seoul but moved to London when he was a child. After his musical education, he moved back to Korea and started composing music for various venues (mostly dramas and movies). Although he had dual citizenship (Korean and British) he gave up his British citizenship so he could serve in the military for mandatory service (Navy back in 2006). He was discharged not too long ago and he married a former Miss Korea.
Yiruma stated that he wanted to make music for the idol group TVXQ / DBSK because he wanted to make music for a talented group unlike Super Junior. Ok, I made that latter part up. Anyways, Yiruma makes some awesome piano pieces (some of the best in the world in my opinion). He made a nice one for K-flow (Kinetic Flow which you can listen to below). If he does make a piece for TVXQ, it's guaranteed to be a hit.
Source: AllKpop