I just remembered I used to hangout in an IRC chat with the creator of Sonique as a pre-teen when I first started to teach myself to code - Sonique being the main competitor to Winamp way back when.
sonique was interesting because most skins ditched 'square-rectangle' all together. Sometimes it was really wacky, like raindrops on your screen. The visulization engine was very milkdrop-y, too.