Most popular genres are K-Pop (Korean Pop), Hip-Hop, R&B, and Dance & Electronic.
Big-Bang
Rain
Wonder Girls

Other popular artists:

Rock: No Brain (Geugeoti Jeolmeum)
Modern Rock: Nell (Letís Take a Walk)
Hip-Hop: Epik High (Remapping The Human Soul)
Pop: Younha (Gobaekhagi Joheun Nal)
Dance & Electronic: Big Bang (Bigbang Vol.1)
R&B & Soul: Brown Eyed Soul (The Wind, The Sea, The Rain)
Jazz & Crossover: Nah Youn Sun (Memory Lane)