ScrollMagic is a jQuery plugin which essentially lets you use the scrollbar like a progress bar.
It's the plugin for you, if you want to ...
... start an animation at a specific scroll position.
... synchronize an animation to the scrollbar movement.
... pin an element at a specific scroll position (sticky elements).
... pin an element for a limited amount of scroll progress (sticky elements).
... easily add a parallax effect to your website.
... create an inifinitely scrolling page (ajax load of additional content).
... call functions when the user hits certain scroll positions or react in any other way to the current scroll position.