Winamp is my choice. For me, it's the best for both MP3s and store-bought CDs. I liked Daum PotPlayer, but I discovered that it's not so good for store-bought CDs. I have a CD that has tracks that have no space in between, and PotPlayer takes over 5 seconds to finally start the next track whereas Winamp just keeps going.
It also has the ability to save as many custom EQ settings as you want, and it also has several Presets as well. You can save your EQ to the Preset List, or you can save it to a file (.EQF)! All you have to do is click the Presets button next to the Equalizer and then you will see the menu appear where you can access these options/features.
I also like several other things about Winamp, but I'll save that for later. :)