I'm surprised that nobody has mentioned the (very old but reliable) Absolute Columns technique: http://24ways.org/2008/absolute-columns/
In my opinion, it is far superior to both Faux Columns and One True Layout's technique.
The general idea is that an element with position: absolute; will position against the nearest parent element that has position: relative;. You then stretch a column to fill 100% height by assigning both a top: 0px; and bottom: 0px; (or whatever pixels/percentages you actually need.) Here's an example:
<!DOCTYPE html>
<html>
<head>
<style>
#container
{
position: relative;
}
#left-column
{
width: 50%;
background-color: pink;
}
#right-column
{
position: absolute;
top: 0px;
right: 0px;
bottom: 0px;
width: 50%;
background-color: teal;
}
</style>
</head>
<body>
<div id="container">
<div id="left-column">
<ul>
<li>Foo</li>
<li>Bar</li>
<li>Baz</li>
</ul>
</div>
<div id="right-column">
Lorem ipsum
</div>
</div>
</body>
</html>