Sino Centre (信和中心)
582-592 Nathan Road in Mong Kok
My first stop was a very happening mall called Sino Centre. Sino Centre is three stories of pure madness and chaos, with numerous, very similar, super small and cramped independent shops. The top two floors have several stalls carrying Kpop albums at reasonable prices. I saw Apink's latest album, Secret Garden, for $110 HKD ($14.19 USD), which is barely cheaper than HMV, a music chain store, which sold it for $115 HKD. I also found a rare item: CNBlue's Ear Fun limited edition Yonghwa version for roughly $450 HKD! This item is so rare, I can't find any online; I've only found Lee Jung Shin's and Lee Jong Hyun's online. These shops carry the latest releases, have usually just 1 copy or so of their merchandise and shop owners know their inventory well. Just a warning, beware: there are some shops selling counterfeit albums, so just be cautious as to what you're buying.
At an intersection of Woman's Street, I found an adorable Etude House! This store is so popular in Asia, while all other Korean beauty brands seem so scarce. This corner location has limited retail space and its layout is like a wide hallway with a 90 degree bend. The exterior detailing matches the typical princess concept Etude is known for, which enchants me every time I see Etude because the design is just so charming!
I didn't spend much time in Mongkok and I know there's a lot more to explore, but these two locations are a great place to start!