qTip is an unobtrusive jQuery tooltip plugin with a list of nice features.
- rounded corner support without use of any PNGs
- very flexible tooltip pointers are as they can be positioned in several locations
- 5 ready to use stylish themes & you can create your own easily
- support for not-overlacking. How close the tooltips are, they will preserve their stacking order
- ready to use effects: fade, slide, glow & custom ones can be created
The plugin is cross-browser & tested in all major bowsers. It is also very well-documented.
qTip has with a scripting API that allows you to easily extend the functionality through a variety of optional callback methods & attributes. So, you can even extend qTip by writing plugins for it.