View a Minecraft skin as a 3D model?

Check out SkinEdit, which will let you edit and view your skin in 3D without constraints. It works for all platforms that support Java: OS X, Windows, Linux, etc.

When you download it, you'll get a JAR file, SkinEdit.jar: you should be able to just double-click on it to launch it. Once loaded, just click and drag on the model in the bottom-right corner to pan around and see your skin in action.