Tooltipsy – jQuery Tooltips For Control Freaks
Tooltipsy is a jQuery plugin that provides a flexible base for creating tooltips.
Compared to other plugins, it comes with minimum default styles or animations but gives you the complete control over them.
It can be positioned however you wish, look and feel can be totally customized with CSS and any type of animations can be implemented.
There are also few settings like "the ability to aligning the tooltip according to the cursor or the element" and "its distance from them".
Tooltipsy is very well-documented and a set of samples show the flexibility offered.