This is a very simple layout (please look at the source or test at all browser widths from as small as possible to more than 1000px):

However, if I vary the amount of content then I get this:

...please particularly look at when the browser is 480-1000 pixels wide on layout2.html.

What's the best way to deal with this assuming the content can be varying levels (e.g. the content may be forum posts or from a DB so you can never know the exact length of it)?