CSS floats made easy (well, almost)
I wrote this post a while back. The content can still be relevant but the information I've linked to may not be available.
After working with cascading style sheets for a while, you soon get to realise that floating elements can achieve many things, but the use of the float property also comes with its own problems. 'How to clear floats' being one of these. Now, Smashing Magazine has published a great article that provides all you ever wanted to know about CSS float theory.
The article has a ton of links that provide help with every aspect of float theory. Great stuff!