I love you for liking 2AM.

Maybe you should check their "mates", 2PM?
I personally recommend:
SNSD/Girls' Generation - YES. they're not as sugary and cute as everyone thinks, they are talented. You should listen to
Oh! album and
Run Devil Run at first.
Gummy - that woman has amazing voice, must listen! her last mini
Loveless is perfect.
Wonder Girls -
Nobody was a huge hit in Korea, nothing shocking, that song is so addictive! and not in western pop style
F.T Island and
C.N.Blue - most famous rock/indie bands. They make great music!
BoA - of course if you don't know her...
SHINee - they stand out from other boybands! IMO. xD and their music is refreshing and a bit different from typical k-pop IMO.
f(x) - only because I'm biased. xD and they were called female version of SHINee... at least you'll love Amber.
Brown Eyed Girls - as Pommy said,
Abracadabra... I add
Sign to must-listen songs.
Lee Jung Hyun - her old techno works are korean classics. You also have to listen to her latest mini, with
Suspicious Man!
Rain (Bi) - at least to know with who Hyori is paired in korean/international fandom.

anyway, every main song (which is performed) in his career is so damn catchy. Don't worry if listening to them will make you feel horny, everybody do
AND HE'S SEX ON LEGS TOTALLY
Big Bang - to check how one of the most popular boybands sounds. And because of G-Dragon you mentioned!
Younha - she's different from other female solo artists... she's like korean YUI/miwa/Mao Abe/put whoever you want. hella talented.
Davichi - girl duo, they have amazing voices! <3
Epik High and
Outsider - most known hip hop artistes.
that's all, others will help with the rest, I'm sure
EDIT: Oh sorry, I didn't understand your first post! ^^' I'm coming with the help:
2AM
I did wrong album
This Song
DBSK
korean
Rising Sun album
O! album
MIROTIC album (try to find repackage also)
japanese
T album
The Secret Code album
latest (hope not last...) singles:
Share The World,
Stand By U,
BREAK OUT! and
toki wo tomete
SHINee
2009, Year of Us mini album
Replay
Juliette
A.MI.GO
The SHINee World (doo-bop)
Love like Oxygen
^ most known songs.
G-Dragon
hmmm... he released one album,
Heartbreaker, but I don't think you'll like it, it's very westernish ^^'
2NE1
they released only one mini album and digital single,
Try to follow me.
Hyori
U Go Girl
Chitty Chitty Bang Bang
Swing