Compared to 3 column layouts, there aren't that many well-commented 2 column versions. Although this is arguably because 2 column layouts are less useful/popular per se, it is just as much the case that they provide less opportunity for flexing one's css muscle. 2 column layouts are simply a subset of 3 column ones.
Any 3 column layout can be made into a 2 column layout. Usually, simply by discarding the third column. The examples on the ThreeColumnLayouts page should cover most situations.
Community MX produces CSS layout templates, called JumpStarts?, that come with CSS fully commented, as well as a bundle of article explaining the techniques used in the layout, and all source files. The North Pole JumpStart? is a free two column, fixed width layout:
[Community MX JumpStart - North Pole]
[The perfect 2 column liquid layout: left menu], [right menu] and [half-half] No hacks!* 2-1 column ordering. Full height columns.
More two column layouts:
[White Cappuccino 2 column layout]
On January 23, 2004, Ryan Brill posted (on mezzoblue.com) a method for creating a two-column layout with a footer by using negative margins. The sidebar follows the main content in the HTML, and neither the content nor the sidebar ever overlap with the footer, no matter which is longer. This method works in IE 5+, Mozilla 1.7+ and Firefox 1+, Opera 8+, and Netscape 7+ on Windows, and Safari 1.1+ and IE 5+ on Mac, and Konqueror on GNU/Linux.
[Ryan Brill's solution involving negative margins]
[Ryan Brill's article on AListApart] June 2004
Unfortunately Ryan Brill's solution immediately fails in the presence of aligned images. Take a look at my page that illustrates the problem. [Page illustrating the problem] (link tried Sat, Jun 10, 2006 and found to be broken - 404 not found - could owner please update?)
I see this as a problem with using the deprecated align attribute, rather than the layout. Float should be used to align images. -- ZoeGillenwater
On October 21, 2005, Alex Robinson posted (on positioniseverything.net) a anyorder method for creating layouts with any numbers of columns in any order. It can therefore cope with 2 columns no problem.
[2columns.net - generates layout with two columns with equal height ]
Pagecolumn's [2 column layout generator].
* "No hacks" except that it requires overflow:hidden which will truncate any text wider than the div.