Leave it to Smashing Magazine.  Awesome ideas for common CSS challenges with the wonderful float property.

I read and re-read the articles below. They are aging but speak to a time when the evil IE6 was even more prominent than it is years later in 2009.

• Top reasons your CSS columns are messed up
• No Margin for Error
• CSS standards (suggestions?)

General insights include:

• Kill IE’s double margin bug with display:inline on a floated items.
• When 2 adjacent elements’ margins meet, only the bigger margin is used.
• If an item’s 2 opposite margins meet, they both go away (self-collapse)
• Nested items without padding or border will cause the top and bottom margins of all to collapse. Left and right margins remain. Adding padding or border makes the margin come back.
• Set overflow:hidden on columns to prevent object blow out in IE.
• To make columns, float:left on one and float:right on the other.
• Self clear an object (always clear floats) with the :after filter.  (Example below.)
• Center an item by setting auto on left and right margins.  margin:0 auto.
• In addition to auto margins, to center an item in IE, also use text-align:center on parent, then reset text-align in child, usually text-align:left.

Self clear example

.columns:after {
content: ".";
display: block;
height: 0;
clear: both;
visibility: hidden;
}

Convert a list into a horizontal menu

Using background images instead of text.  Fixed width, left margins, using negative margin on UL to cancel first margin.

<ul class="menu">
<li><a href="#somewhere1" id="link1"><em>link 1</em></a></li>
<li><a href="#somewhere2" id="link2"><em>link 2</em></a></li>
<li><a href="#somewhere3" id="link3"><em>link 3</em></a></li>
</ul>


ul.menu {
margin:0 0 0 -20px;
float:left;
width:100%;
}
ul.menu li {
list-style-type:none;
display:inline;
float:left;
margin:0 0 0 20px;
}
ul.menu li a {
display:block;
height:50px;
background-color: #0f0;
}
ul.menu li a em {
display:none;
}
ul.menu li a#link1 {
width:100px;
background-image: url(link1.png);
}
ul.menu li a#link1:hover {
background-image: url(link1-over.png);
}
ul.menu li a#link2 {
width:110px;
background-image: url(link2.png);
}
ul.menu li a#link2:hover {
background-image: url(link2-over.png);
}
ul.menu li a#link3 {
width:120px;
background-image: url(link3.png);
}
ul.menu li a#link3:hover {
background-image: url(link3-over.png);
}