One Column Theme
WPTouch is a complimentary theme installed as a plugin on your WordPress blog or website that will format your content with this Apple-inspired, full-featured theme when your visitors are using an iPhone or iPod touch.
Two Column Themes
Hanami is a two-column widget-ready theme, inspired by the WP Admin palette and the Seed Conference font-stack. Simple and clean, the theme displays content in clear and concise manner.
Simple Blog is a simple theme, 2 columns, widget-ready with Gravatar support for comments.
Lean and Clean is a two column widget-ready theme. The size of the content area and the sidebar is almost same.
K9 is a two-column widget ready theme based upon the popular K2 theme. The theme works only on WordPress 2.5 and above only.
Three Column Themes
Midnite is a 3 column, widget-ready, cross-browser friendly theme compatible with WordPress 2.5.1.