jScroller is a stylable scrollbar built using the jQuery JavaScript framework. At only ~8kb, it is both lightweight and packed full of features.
It can scroll any sort of HTML , and has heaps of features, such as: vertical/horizontal scrolling, automatically resizing scroll handles, support for mousewheel. It is also very easy to create your own theme.
You can set the amount to scroll with the mouse wheel/arrows, and can interface with its easy to use API in order to change an option(s) on the fly and/or scroll the scroller (as shown in the examples).
You can set the scrollbars to only show when the scroller is hovered over, and when horizontal/vertical scrolling is no longer needed, they will even hide themselves!
Check out the demo for some examples of jScroller’s features and how to use it.