You can listen to Pray by Sunny Hill. It has a nice MV and I liked the music and lyrics too.
There is also Mistake by SNSD.
Cry Cry by T-ara.
Sorry, Sorry (ANSWER) by Super Junior (This one is slow, not really sad.)
One Kiss by Jaejoong, All Alone by Jaejoong
Love Song by BIGBANG
Obsession by SHINee
Sorry I'm Sorry (Love this one) by Kim Hyung Jun
Sorry That I'm Sorry by Kim Jin Pyo (Ft. G.NA)

~LINKS~
Pray by Sunny Hill: http://www.youtube.com/watch?v=iZUsqow_OTc
Mistake by SNSD: http://www.youtube.com/watch?v=t7nWaLWSTqg (No MV for this song at all btw) Cry Cry by T-ara: http://www.youtube.com/watch?v=s0SrFr2x_pc
Sorry Sorry (ANS.) by Suju: http://www.youtube.com/watch?v=10INLIBrLT0
One Kiss by Jaejoong: http://www.youtube.com/watch?v=XsD6k9SRIIA (No MV, again.)
All Alone by Jaejoong: http://www.youtube.com/watch?v=RbbJEDZurnA (No MV)
Love Song by BIGBANG: http://www.youtube.com/watch?v=jpy1LDuk8AQ
Obsession by SHINee: http://www.youtube.com/watch?v=w7weBW57yqE
Sorry I'm Sorry by Kim Hyung Jun: http://www.youtube.com/watch?v=l_3z5OM4eYY
Sorry That I'm Sorry by Kim Jin Pyo (Ft. G.NA): http://www.youtube.com/watch?v=0g_Vr3Y8S2E

Hope this helps!
The links above bring you to each song's respective Music Videos, and they're ALL subtitled in english! I hope that these songs are of your liking, because I pulled them all out from my own library. Have fun! ^^~