While there are the skull heads that you can get from mobs, there are also a lot of decorative skull heads that were uploaded as player skins.
The /head command can be used in-game to spawn Minecraft heads found on minecraft-heads.com.
- Find a head that you like on the site.
- Click on the head name to go to the page for it.
- Use
/head URLwhere the URL is the page URL.