I recently recommended Thesis from DIY Themes.
Since then version 1.1 has been released, which includes a whole new design options page where you can change the font sizes of the nav, titles, content and footer, as well as change widths and the number of sidebars without having to deal with the CSS. Pretty handy!
Just this weekend if you buy Thesis you can get the magazine theme Cosmo for free (when it’s released)!
Check out the Copyblogger Thesis update and Pearsonified for more info.