Gecko, Trident, Webkit CSS Extensions:

Unique vendor extensions on a p/browser basis offering more CSS flexibility

Extension Organization Documention
-ms-, mso- Microsoft (Trident/Internet Explorer) URL / -ms-filter specific
-moz- Mozilla (Gecko/Firefox) URL
-o-, -xv- Opera Software (Opera) URL
-atsc- Advanced Television Standards Committee
-wap- The WAP Forum
-khtml- KDE (Konqueror) URL
-webkit- Apple (Webkit/Chrome/Safari) URL
prince- YesLogic
-ah- Antenna House
-hp- Hewlett Packard
-ro- Real Objects
-rim- Research In Motion
-tc- TallComponents

- Source:

Useful Print CSS

Note about puesdo:classes
In Internet Explorer, there must be declared a <!DOCTYPE> for the :hover selector to work on other elements than the <a> element.

Other Useful Resources:

CSS3 Examples