Winamp Skins
Winamp was a versatile, all-purpose music player that was very popular in the late 90s and early 2000s. It was easily customizable, both in the playable audio formats it could handle with plugins, and in its appearance with skins. There are literally thousands of different, unique skins available for the player, many of which were hosted on personal websites.
I've collected a large amount of Winamp skins over the years (at last count, I have 437 of them...) and since these files are so small, I've uploaded my entire collection here in case anyone is interested in using them. Though, I wonder how many people visiting this site are interested in using an old, deprecated music player... or even have any music files to play on it what with streaming being a thing... I guess someone with a weird affinity for old software would be interested in this!
The skins are available for download as a zip file here: Winamp Skins.zip
Here's a few of my favorites:
Links
The best place to go to get Winamp skins nowadays is the Winamp Skins collection on the Internet Archive. It's an ongoing project to archive as many skins as possible from various sources!
Winamp Skin Museum - A visual interface designed to easily browse, search and test out the skins in the Internet Archive collection. I recommend going here if you're looking for skins to download!