MineSkin.org allows you to generate skin texture data signed by Mojang.
These can be used on ingame skull blocks or to change a player’s skin using some packet magic :).

This website makes custom skins a lot more convenient and less time consuming, since it uses multiple accounts donated by multiple awesome people <3.
This way, you don’t have to use your own account to generate textures
and you can get your custom textures within seconds, without going through the hassle of changing your own skin, etc.
If you’d like to make things even faster, please use the Account Manager 🙂 (more details)