SmashingApps comes up with an awesome list of 21 Mindblowing Premium-Like Free WordPress Themes.
This is quite impressive and covers an array of different layout styles. From the site:
This is not the long list with all the available wordpress themes on the internet but its an exclusive collection of free wordpress themes which are not less than premium themes and you may consider any of these themes as per your need before going to purchase any paid premium theme.
Below are screenshot of some I found the most impressive looking. Be sure to visit SmashingApps for the full list, descriptions, and breakdown.