Sunggyu used to be in a rock band before Infinite, and is very open about his music taste.
Here's a sample of what is probably on his ipod based on interviews he's had:
Nell - Farewell
This entire album (Healing Process) Sunggyu is a HUGE Nell fan and talks about this album constantly.
Ne-Yo - Because of You
Sunggyu often covers Ne-Yo songs because their tones are very similar! He originally didn't like R&B but Ne-Yo helped him get into it :D
The 1975 - Somebody Else
At the end of the day, Sunggyu will always be a rock fan. The 1975 is the perfect blend of rock, pop, and dance that is right up Sunggyu's alley. (Song starts 3 minutes into the video)
Justin Bieber - What Do You Mean (Acoustic)
Like Ne-Yo, Justin Bieber has a similar tone to Sunggyu and he often covers Bieber songs!
Cherry Filter - 오리날다
This is a Korean throwback and was a super popular pop rock group that most people Sunggyu's age remember and love!
언니네 이발관 - 천국의 나날들
언니네 이발관 is actually one of my favorite Korean indie groups and I highly recommend them. Some of their albums are very similar to Nell so Sunggyu listens to them a lot too!