Mouse over effects are quite useful and even look good. A mouse over effect is basically what happens when you mouse passes over an object, ussually a picture and that picture changes.
In this example two images are used. And if you want to do it properly you have to have two images that slightly differ from one another.
<a href="http://oregac.googlepages.com" title="home"><img onmouseover="this.src = 'http://oregac.googlepages.com/homeover.png'" onmouseout="this.src = 'http://oregac.googlepages.com/home.png'" src="http://oregac.googlepages.com/home.png" alt="Home"></a>
This code produces the following effect:
Quite handy for menus. A whole menu can be made just by using images and the mouseover effects.
I have not figured out yet how to make an onClick image change but will try to find it if it can be done. If the effect does not kick in directly wait a bit as the picture needs to be loaded.