Platform is a beautiful free framework theme for WordPress from PageLines. One of the themes biggest selling points is the ability to drag and drop content areas. This allows you to easily build the site structure you need.
A pro version of the theme is available for $95 however the free version should be sufficient for most of you.
Platform has a tremendous options area which allows you to customise how your site is structured and what is displayed (though not as many as the Suffusion Framework Theme).
The biggest area of the options section are the template setup and layout editor. In the layout editor you can choose the type of structure i.e. where the sidebar goes and how many columns etc. The template setup allows you to drag and drop content to where you want.
In October I raved about the Suffusion Framework. From a customisation point of view I believe Suffusion is better though Platform will have more than enough features for most people and has a much better design in my opinion.
I encourage you to check it out if you want a bit more control over how your site is structured :)