CNBLUE (from left to right: Jungshin, Minhyuk, Yonghwa and Jonghyun)
They are one of the most popular K-pop bands. Considered as The Beatles of Korea. I've been listening to their songs this past few days and I can say that I consider them as the second best K-pop groups behind SNSD.
Recommended songs (to those who listen or have interest in K-pop):
I'm a Loner
Still in Love
Mariah, Celine, Whitney The Vocal Trinity
Aaliyah, Nelly Furtado, Katy Perry, Lady Gaga
Girls' Generation - EXO