Smooth Parallax Scrolling
Quoting from kirupa.com:
For many practical reasons, our UIs are designed to be two dimensional. Once you throw in meaningful content, some navigation, and other doo-dads to make your application usable, adding any more dimensions simply gets in the way and becomes a distraction. Despite the stranglehold two dimensions have on what we create, there are subtle and effective ways of sneaking an extra dimension in here and there.
Follow this link for a nice article about implementing smooth Paralax Scrolling effect that also works with the mouse wheel.