One way I can think of would be to give every other div (div numbers 3,5,7,9 etc...) a seperate class, and then you add clear:left; to that class.
The other way would be to wrap every 2 DIV's in another DIV so the next one forces below the largest DIV e.g.
Code:
<div id="container">
<div>Some Text</div>
<div>SomeText</div>
</div>
<div id="container">
<div>Some Text</div>
<div>SomeText</div>
</div>
First method requires an extra class, second method requires a bit of extra markup..