There are many recent top artists.
Some of the older ones are Wonder Girls who was Korea's top girl group because of their hit song Tell me and So Hot.
But now, SNSD has taken over and owned 2009 with their two VERY hit songs Gee and Genie, with Gee winning 9 weeks in a row which broke a record. SNSD has comeback with a new song OH! which is receiving lots and lots of love. Their Oh! Album has sold heaps of copies :D Songs that i recomment listening in SNSD. Fast songs: Gee, Genie, Oh! Into The New World (debut song) Slow Songs: Dear mom, Star Star Star (new song in OH! album), Forever (new song in Oh! Album), Saring In Gul Yo (Taeyeon and Sunny), One Year Later (jessica ft. SHINee's Onew), By Myself (Tiffany), If (Taeyeon), Oppa Nappa (Jessica Tiffany Seohyun - second third fourth best singers named as the JeTiHyun trio)
2NE1, a new rookie group but became REALLY popular due to some of their songs fire, i don't care, with i dont' care being one of their top songs.
KARA is really popular too and may even become more popular with their awesome new song Lupin :D
Guy bands such as Big Bang which has many hit songs, they also sang Lollipop with 2NE1, 2PM - heartbeat, again &again has been quite popular, Super Junior was always popular but also with their hit song SOrry Sorry in 2009 and SHINee with RIng Ding Dong, SS501 with Love Like This
You can find all these songs on Youtube