Two-column themes in my opinion offers more room for readability and does not hinder with widget availability. Get as many widgets as you like and keep posts readable – the best of both worlds. Moreover, it sports a cleaner, more professional look than a three-column design. That is why successful bloggers use this kind of theme as it offers them flexibility in design like no other.
There are a lot of 2-Column themes out there but these are probably one of the best out there. WPHacks compiled the best 2-column themes with screenshot for us to enjoy and wonder. I assure you, everyone will have their own favorites.
Full article here: http://wphacks.com/best-wordpress-2-column-themes/