Jabbarocky - Lots of Sandman, plus some anime. Fruity Candies - A small collection of mostly sh jo winamp skins. Lots of Watase Yu artwork. A skin for XX - Brand new site, interesting skins. There's some anime, too.
Some skins are beautiful, some are crap.
Awesome designs, really. Fyre Skins - Where half of the skins I regularly use come from. The other half of my set of alternating skins comes from this site. Audiogalaxy - Our favorite source for mp3. Once you have Audiogalaxy, you have pretty much all you need.