If you only go around the town area, you can try sembawang at plaza singapura. Not sure about other sembawang, music junction or CD ramas in the area
I don't go there to buy CDs. But they definitely offer ayu, kuu, namie and hikki CDs at lower prices than HMV. Recently, it seems that some of the more popular Johnny bands and oddballs like leah dizon are also sold in these stores. You can go check it out. But if you're looking for something like mr. children or j-rock bands then HMV is still the place to go.