CSS: How to create an horizontal navigation CSS menu with mouseover effect

The first time I achieved this effect (about 6 years ago) I felt just like when I found a $20 dollar bill on a jacket I hadn't worn in 1 year. I know it's simple, but for a beginner, it's the beggining of the path to CSS Wonderland. The code will be easily customizable. After you go over this tutorial I suggest you start playing around with the code by changing color, padding, font-size, etc.