Well, I'm partial to Hip Hop and R&B.
Ok. I've got to run now, but I'll look at making some suggestions when I get back tomorrow.
People have already made plenty of good suggestions (I want to highlight Dynamic Duo and Epik High as well as Gaeko & Tablo's solo stuff - fantastic songs and albums over many years), and since Korean hip hop and r&b artists collab with each other so much you'll probably come across someone you like that
isn't mentioned here, but here are a few more:
Zion. T
Two Melodies (ft Crush)
Yanghwa Bridge
Babay (ft Gaeko)
(Released "OO" album this year which was great, but imo "Red Light" from a few years back is better)
Beenzino
Dali, Van, Picasso
How Do I Look?
Break
("24:26" is his best album)
Peejay
He's a producer rather than a rapper/singer, so gets people working on his tracks, but "Walkin' Vol 1" (single - "
I Get Lifted (ft Beenzino)") and "Walkin' Vol 2" (single - "
NA B YA (ft Zion. T)") have been some of my faves over the past few years.
Giriboy
He gets less recognition and chart hits than some of the people here, and is better known for his collab songs with NS Yoon-G and Soyou, but his albums "Adult Ceremony" (aka "Sexual Perceptions") and "Mechanical Album" are very solid (especially Adult Ceremony)
Heize
The newest chart queen
And July (ft Dean, DJ Friz)
Don't Know You
Star
Crush
Outside (ft Beenzino)
Just (with Zion. T)
Woo Ah
On the idol group side of things, in addition to the aforementioned Big Bang there is 1 group I will highlight as having better used hip hop in their music than other groups -
BTS.
Singles (public friendly)
Danger
War of Hormone
No More Dream
Non-singles (where they can turn up the hip hop)
Cypher Pt 3
Baepsae