Haha, the list has to be long, because they have many good songs! :)
Mh, my favs...difficult question.
- Good Person (좋은 사람), Don't leave (떠나지마), Falling U, I am really hurt (내가 너무 아파), Ma Boo, Day By Day, Lovey Dovey...
But as I said, I could easily name at least 10 more songs, which are equally good. That's why T-ara is one of the few core K-Pop artists I still listen to a lot. ^^
Ah, and I have to mention "We were in love" (Collab with Davichi) - amazing song, beautiful/strong vocals.
Btw, SL is by no means a bad song (5th place in play count in my library), so I totally understand that people love it. It's damn catchy. I just have enough of it at the moment. ;)